Currently, the “Maximum interval” sets a fixed number of days that card’s interval can get to. In an old deck with plenty of long interval cards, several cards in a row upon review can hit the maximum interval. If you are reviewing a deck after a bit of a pause, you can end up with hundreds of cards scheduled to appear in a single day in the future.
Making “Maximum interval” a range (e.g. 1000-1200 days) will prevent this from happening.
Unless the range is really large, most cards would still be assigned the maximum interval. In your example, given an ease of 250%, only cards with a previous interval of 400 to 479 days would be assigned an interval below 1200 days, compared to all the cards with an interval between 480 and 999 days.
I’m not sure how fuzz is currently handled for cards with a maximum interval, but wouldn’t this small amount of randomisation applied to every new interval be the simpler solution?
I’m not sure I understand the first paragraph well, but I imagine it like this: when a card is reviewed and it has a new interval ≥ 1000 days, e.g. 1000, or 10000, it is assigned instead a random interval between 1000 and 1200 days.
I am not sure at all how fuzzing is done, but from what I can see in my deck, judging by how there are huge spikes of reviews in certain days in future, there’s no fuzzing applied to the maximum interval whatsoever. Perhaps if the regular fuzzing is applied to the maximum interval, that would do just as well, and perhaps would be covered by the load balancer, too? Or maybe the fuzzing would result in too large of a date range?
The interval cap is applied after fuzzing; to do otherwise causes users to complain that their cap is not being respected. If you’re willing to tolerate cards being scheduled above your cap, then increase the cap. 
It makes sense to apply a cap after fuzzing if it’s a single number of days. If it’s a range, users would expect the fuzzing so they won’t complain (hopefully~).
I am willing to tolerate cards being scheduled above my cap, just not when it’s on the order of several years…
I have a similar issue, and would appreciate the proposed solution. Is there any way of doing this?