Well, it's feasible. For instance, there is a reader called TomeRaider for which you can get pre-compiled Wikipedia files. The full English edition 12/2004 was about 500MB compressed.
Check out this thread for more:
https://www.mobileread.com/forums/showthread.php?t=3129
I think MobiPocket has a fairly decent compression ratio as well. You might want to use one of their desktop applications to convert html to Mobipocket.