NEW YORK (MarketWatch) — Investors are nearly giddy over the European Central Bank’s meeting on Thursday, penciling in expectations that Mario Draghi will announce an aggressive program of government bond purchases in an effort to beat back a deflationary spiral that threatens the eurozone.

But the potential for disappointment appears to run high. The euro fluctuated wildly Wednesday, after The Wall Street Journal reported that the ECB’s Frankfurt-based executive board would call for bond purchases of roughly 50 billion euros ($58 billion) a month for a minimum of one year. The proposal would serve as the basis for deliberations by the ECB’s governing council on Thursday, which could substantially alter the plan.

Still, the euro EURUSD, -0.06% is trading near its lowest level versus the dollar since 2003, while eurozone government bond yields have fallen sharply in anticipation of full-fledged quantitative easing. European stock indexes were mixed Thursday, but have rallied in anticipation, with Germany’s DAX index DAX, -0.69% nabbing a new record close and the pan-European Stoxx 600 index SXXP, -0.66% hitting a fresh seven-year high on Wednesday.

The eurozone’s toxic internal politics and the design flaws inherent in shared-currency project could make it difficult for Draghi, the ECB president, and his colleagues to craft a convincing solution.

Here’s a look at ways investors could be left disappointed once the dust settles.

Too little

Scope for disappointment? RBC Capital Markets

Needless to say, other market watchers argue more detail, not less, will be needed to prevent market disappointment.

“The real test for the ECB is the size of the program.,” said Kathy Lien, managing director at BK Asset Management. “In order to impress, the ECB needs to commit to buying a trillion euros worth of sovereign bonds or more. Investors are already questioning whether €500 billion will be sufficient to drag the [euro zone] out of its sluggish state of growth and low inflation.”

The executive board’s proposal suggests bond purchases would amount to at least €600 billion in total, while Bloomberg reported that purchases could continue through the end of 2016, injecting as much as €1.1 trillion.

The market’s reaction to the reports, with the euro rallying on what traders described as an apparent short-covering squeeze, suggests investor expectations are running very high, making it unclear whether €50 billion in monthly purchases would leave investors satisfied.

Too fragmented

Eurozone government debt by issuer. HSBC

According to some news reports, the ECB is likely to strike a compromise aimed at addressing German misgivings over outright quantitative easing. According to the Financial Times, the move would see the eurozone’s national central banks buy sovereign debt issued by their national governments; responsibility for any losses on those debt holdings would remain with the national central banks.

This could be problematic, writes Janet Henry, economist at HSBC.

A program in which national central banks buy their own country’s bonds and hold them at their own risk probably wouldn’t diminish the effectiveness of QE, she wrote, but it risks leaving investors with the perception the program “had been designed in a way that would make it easier to facilitate a eurozone breakup further down the road.”

Moreover, such a plan would compromise the principles of having a shared monetary policy in which risks and rewards are shared alike, noted James Ashley, chief European economist at RBC Capital Markets.

Another eurozone ‘fudge’

On the menu? Glenn Price/Shutterstock

Indeed, such political considerations have left the ECB with a much more complicated path to full-fledged QE than was ever faced by the U.S. Federal Reserve, the Bank of England and the Bank of Japan.

In the end, this makes it very difficult for Draghi to thread the needle and avoid either angering Germany and its allies on the ECB or disappointing investors who are looking for bold action. The final outcome could be another eurozone “fudge” that leaves everyone unhappy.

“A larger-than-expected sovereign bond-buying program with a bigger-than-expected risk-sharing component is a red rag to a German bull, while a smaller-than-expected one with less risk-sharing would rile markets,” said Nicholas Spiro, managing director at Spiro Sovereign Strategy, in a note.

“A compromise - which is what’s likely to happen - could satisfy neither Germany nor the markets.” Spiro noted.