Fidgeting around with what the reputation mechanic could do/mean.

That's a bizarre way to say "whenever a legendary permanent etbs under your control"

Yea, in this particular application that's what it amounts to. This is just one possible application. The idea to me is for the mechanic to have multiple applications based on the number of legendary permanents you control. This route does come off weird because of the wording. My original intention for it is more along the lines of "equal to your reputation" or using it as an adaptable number for things like converted mana cost or any other number relevant to gameplay.

FWIW, I think reputation is a cool concept.

I think a lot more interesting things can potentially be done with it than this route. And it definitely has some cool flavor as well.

I think the whole concept and the mechanics being toyed with for this set would create a pretty interesting format, with not just a lot of "superfriends" going on, but such an emphasis on legendary stuff that it would significantly impact the way people play and build decks.

I'm just starting to toy with what can be done with the mechanics and feeling out if they're viable. I've yet to mess with Conjure (Your planeswalkers may help cast this spell. Each loyalty counter you remove from a planeswalker you control while casting this spell pays for or one mana of that planeswalker's color.) I'm not sure this will be as viable as Convoke, but in a set like this it may be okay.

Legendary Landcycling seems like a nice fit even if it seems super niche. And adding legendary instants alongside legendary sorceries. With all these mechanics together, pretty much anything can be legendary and "legendary matters" can more easily mean something.

My stab at toying with a Planescape set from a few years ago hit a brick wall with a weird mechanic and tried to go more a "land matters" route, but I think "legendary matters" is better, which also overlaps with "planeswalkers matter" and leaves room for legendary lands mattering too.