It's not a bad idea, just not a practical one. Firstly, the wiki will almost certainly be too big, and you really don't want to be putting *anything* on the NAND that isn't absolutely necessary.
Also, the wiki is only barely keeping up to date with things as it is (not that Esn et al. aren't doing a great job, though), so I doubt we want to be putting more pressure on the maintainers by changing to EvoPedia. Even if we did manage to move without too much trouble, the user would then need to keep downloading new versions of the wiki as it is constantly being updated, or have a dynamically generated firmware using the latest version.
And after all of that, this will cause a lot of people to think what they have on their NAND is the be-all and end-all of advice, and not check the more recent online version.