It's also possible that the fetches will cost more life than the original cycle, especially being enemy colored. Fetching basics is another interesting option.

That would actually be a little bit interesting, at least, if the enemy fetches were worse than the originals, because there'd at least be some tension when constructing a manabase. If they just straight up printed a U/G Fetch, the manabase would be simple:

4 UG Fetch
3-4 UW Fetch
1 Forest
1 Plains
3 Islands
4 Tropical Island
3 Tundra

On the other hand, if the new fetches cost two life, there might be some debate about how many to run. Probably a lot, anyways, but at least there'd be a question about it.