Excellent idea. "Number of matching lands" is something that could be done on an artifact but is hopefully better on a fortification. There are "number of mountain" cards, but this is a decent way to make one that works with any color deck.

(It probably should be some other effect than "gain life", though: as a one-off, gaining life is a good choice for scaling with number of lands, but I think gaining 4+ life a turn is too good for common, as it's too hard for your opponent to actually win.)

Hachee Machie. I do like the mechanic, but this implementation is too strong at any cost in common. Also, I'd push for this to say "At the beginning of your upkeep, for each land that shares a type with the fortified land..." I mean, unless we're planning on designing lots of cards that untap lands and/or plan on putting a number of Stasis type cards in the set, it won't be hard to untap every land you control every turn... so why not jump to the point?