Bahamut, Odin, Jeanne D'Arc, Lancelot, Ancient Elf, and Tiamat.
Literally one day after I post in comments that people have been talking about this forever and they still haven't brought it over...they bring it over.
Fortunately at this moment the cards that can evolve into five seem to be restricted to SR and up. Now, the question I pose is, is it worth it? As far as I can tell, kind of. Although the stats only increase by 1500 or so, you have to consider a player doing this probably already has the 4max version of the card. For the price of one more of them they can increase their power.
Its up to each individual player, but given the current selection of cards that can be increased, I would only consider Lancelot.
So how does this effect you?
Chances are it doesn't. The cards chosen at this moment will offer mild increases in very high level decks. Most players have decks primarily composed of HR and many of those same players have opted to skip SR and move into SSR.
What these changes have done for players who are moving up is allow them to invest into an SR and eventually bring it up to just under SSR power levels. In essence these cards are becoming SSR 2.0 not legends. All of the other true legends outclass them.
Are these changes good or bad?
Good. As long as they don't try to apply it to every rarity and keep it for the highest. This fifth evolution offers players something that bridges the long and expensive gap between SR and SSR.
Personally, it's something that I don't intend to engage in because I don't see the point on spending a bunch of HP to create a Legend card that doesn't have a Legend buff. If they increased the buff power on the fifth card, I think it would be worth it.
So, recap. You get about 1500 additional stat points from what I've seen and no increase in buff power. Is it worth it? In my opinion not really.