The minimum median block size is current 20 KB, meaning without the dynamic block size kicking in, any block can be up to 20 kilobytes without any miner penalty. In increasing the block time to two minutes it was initially proposed to increase the minimum median size to 40 KB, which retains the same rate of base block capacity.

It was later proposed to increase this to 60 KB, because of the observation that larger mix sizes will create more split transactions and split transactions are inconvenient for merchants, whose systems are often set up to accept one payment, and further sometimes find payments need to be processed manually due to various problems with split payments. 60 KB is observed to allow most routine payments to be handled without splitting.

So the current plan is to increase the minimum median block size to 60 KB. As a rate this is 300 KB per 10 minutes, so 30% of Bitcoin's maximum rate (1 MB/10 minutes), though of course Monero allows the block size to increase based on transaction demand. The minimum size reduces the resistance to spam attacks and increases the potential for more rapid blockchain growth relative to transaction demand.

It is not necessary to increase the minimum block size at all. In AEON when the block time was increased from 1 to 4 minutes, no increase in the minimum block size was made, and everything still works, with the block size dynamically increasing during high usage. However, this does not provide any relief from the need for many split transactions, and further AEON does not impose a hard minimum on mix factors the way Monero will (post-fork).

Open for discussion or feedback on the proposal to increase the minimum median block size to 60 KB.