Hm. I don't like "on target basic land you control". That means two or three of these are close to worthless, and in fact the card's only worth playing in a deck where at least half your manabase is basic lands. The Firewild Borderpost cycle had that problem too.

I've been looking at that, and I'm starting to think it needs to be "on target non-district land". The inherent problem in allowing where the development counters can go is that if they are put on districts, then each district has the ability to be City of Brass with no drawback, making the proper land mix "twenty districts".

My goal is to create another color-fixing cycle (the set as a whole works better with good color accessibility) that feels like something completely new and appeals to the more "modern era" setting of the set. I like the idea that there are urban areas that are able to expand over more undeveloped areas, and that land destruction strategies might have a harder time controlling that "urban creep" effect; blow up a either a district or a developed land, and any other new district virtually negates your play.

"Non-district land" would be okay; reminiscent of Treva's Ruins and friends. But I don't think "20 districts" would actually be that strong; you'd still only have a 4 in 20 chance of drawing any one particular colour, and that seems a bit low.

Here's a pretty relevant question: are there any notable permanents that leave "proprietary" counters behind if the permanent goes away?

There are a few cards that leave a counter that has or represents an effect (Aven Mimeomancer, Obsidian Fireheart), and many that deliberately end the effect and remove the counters. I can't remember if there are any that leave a counter that may have an effect later but doesn't at the moment, but so long as (a) you put them on lands, and (b) it's a major theme of the set which lands have them on, I'd think it's probably fine.

I don't know that I'd call it a "major" theme. At this point I see a cycle of uncommons and perhaps a mythic (representing the Debronian capital city, or maybe the Soradyne Corporation Building... Or maybe both).

In the long run, I'm seeing potential for cards in any eventual follow-up sets to also use "developed" lands. The potential for rich story-and-game linkage here is just really deep, and if the stranding of counters is permissible, very easy to execute. Still, I'm concerned that rules junkies are going to go apeshit over this kind of device.

I don't think rules junkies would care. But I suspect MaRo would have a "smoothness of gameplay" objection, something like: I've blown up both your Districts. But you still have to keep the developed-Plains separate from your other Plains, and the developed-Forest separate from your other Forests, just in case you manage to draw another card that makes them relevant.

It is a judgment call; you could end up deciding it's okay. But be aware of that one possible objection.

If this gets MaRo riled up and talking about this the next time I see him, I'll have at least gotten that much right.

Besides, little Monopoly houses and hotels on my lands look awesome.

I agree that the concern is not rules. (And that monopoly houses will make great counters.)

What Alex describes is definitely the problem, if anything. I think it's much less evident than it might be because (i) you rarely will get your land destroyed (ii) even if you do, your lands are unlikely to have any other sort of counter on, and it's unlikely to matter which you tap unless you know you're about to play another development land (iii) lands are easier to keep track of (iv) you may well play another land.

So it's definitely a potential problem, but it may or may not be an actual problem.

The chance of playing another land that cares about the counters is what I meant by a "major" theme. If that's fairly likely, and keeping the counters around is not too onerous, then it's not a big problem. If you may only have one development land, it would be much more annoying, except then, you're probably much less likely to have it destroyed, so it doesn't matter as much.

If having a counter on the lands presents a problem I suppose they could be given the Tendo Ice Bridge solution. Still, I don't think it'll be that confusing most of the time.