Jeff Passan breaks down some of the rule changes that are being proposed in Major League Baseball. (0:52)

Major League Baseball and the MLB Players Association are discussing potentially drastic changes to the on-field game and economic landscape of the sport in the middle of a collective bargaining agreement, a significant departure from the past that speaks to the chasm between the parties but represents a thaw in the chill that has divided the sides, sources familiar with the talks told ESPN.

Dueling proposals from MLB on Jan. 14 and the union on Friday covered a wide range of topics, according to sources. Among them include:

A three-batter minimum for pitchers

A universal designated hitter

A single trade deadline before the All-Star break

A 20-second pitch clock

The expansion of rosters to 26 men, with a 12-pitcher maximum

Draft advantages for winning teams and penalties for losing teams

A study to lower the mound

A rule that would allow two-sport amateurs to sign major league contracts

With owners meetings set to begin this week and spring training next week amid another tepid free-agent market, the willingness to bandy about ideas -- and the openness to addressing concerns -- is seen as a step in the right direction by both sides. Whether any substantive change comes of it, sources said, remains unclear.

The three-batter minimum for pitchers, first reported by The Athletic, is perhaps the most controversial measure, as it would ostensibly eliminate a job created by modern bullpen use: the one-out left-handed reliever. MLB's proposal of the idea illustrates the league's concern with both time and pace of game, as constant bullpen shuffling has contributed to the average game time lasting longer than three hours. The rule would apply to all pitchers, except in instances in which pitchers finish an inning or are injured, sources said.

The union did not strongly oppose the idea, according to sources, instead suggesting it preferred the implementation to be delayed until 2020 rather than 2019, as MLB proposed.

The league's other bid to deal with pace of play was the enactment of a 20-second pitch clock, something commissioner Rob Manfred can put into place unilaterally. While numerous players have spoken out against the pitch clock, the recognition that Manfred has the ability to mandate it, even without the union's support, gives him leverage on the issue, according to sources.

In the discussions, the possibility of the clock being turned off when runners are on base was raised, sources said.

One of the union's counterproposals was the adoption of the designated hitter in the National League, according to sources. While a compromise could be the rule being eased in, the union is advocating for a universal DH in 2019, sources said.

In addition to the universal DH, the MLBPA is interested in changes that would use draft picks to incentivize winning and grant players the ability to earn additional service, which could allow them to hit free agency earlier and theoretically counteract what the union believes is the manipulation of service time by teams.

Low-revenue teams that succeed -- whether by finishing above .500 or making the playoffs -- would be given greater draft positions or bonus pools under the union's proposal, according to sources. While the depth of the penalties were not clear, the union suggested teams that lose 90-plus games in consecutive years could be affected negatively in the draft.

In the wake of Oakland Athletics first-round pick Kyler Murray potentially leaving behind baseball to pursue an NFL career after a Heisman Trophy-winning season, the union also suggested the idea of bringing back the major league contract as an enticement for two-sport athletes to stick with baseball, sources said. Currently, all draft contracts are minor league deals subject to a draft pool that penalizes teams that exceed it.

Athletics draft pick Kyler Murray recently announced he's entering the NFL draft. The MLBPA has suggested bringing back the major league contract as an enticement for two-sport athletes to stick with baseball, sources said. Thearon W. Henderson/Getty Images

Service-time issues remain a key concern for the union, according to sources, with teams capable of keeping major league-ready players in the minor leagues without recourse. While both sides acknowledge service time is a difficult problem to solve, the union's proposal included the possibility of additional service time for performance, playoff appearances or awards, according to sources.

Among the union's ideas was a single trade deadline before the All-Star break, sources said. Currently, the non-waiver trade deadline is July 31, and players who pass through waivers can be dealt until Aug. 31. An earlier trade deadline could force teams to emphasize the first half, which might force them to focus more in the offseason on acquiring players via free agency to improve the likelihood of that rather than allowing them to strike well past the 100-game mark.

MLB's carrot in its proposal was an expansion of roster size from 25 to 26, creating 30 new major league jobs, according to sources. The offering included a 28-man limit on September rosters and a maximum of 12 pitchers during non-September games, sources said.

The league also is interested in studying mound height, with the potential for Manfred to implement a lowering of the mound in 2020, according to sources.

Another league proposal would end all spring training games that are tied after 10 innings and use spring training and the All-Star Game as testing grounds for the rule that starts a runner on second base in the 10th inning of a tied game.

In typical bargaining sessions, dozens of ideas are offered, considered and placed on the back burner, so the likelihood of a handful of these proposals being ratified, let alone all of them, is unlikely, according to sources. Still, as MLB and the union seek to find a place of understanding amid a winter chill that has fractured already-tenuous relations, the mere discussion, sources said, is considered a positive.