If there are that many servers then surely like you said they could try introduce some of the higher level teams into the server. Otherwise introducing some 5-6* bot teams may be worth a shot. But most ideas though seem to consist of there needing to be an influx of teams.

One other idea would be to introduce a level cap and follow real life football league system.
So for example, let's say level 46 is the limit, teams in that level can not be promoted any further but the bottom 3 teams can be relegated (so relegation would have to implemented throughout). They could also impose financial and player implications of being relegated like players do not gain a star by being relegated (to deter those that may think they can gain a star). Player quality could potentially stay the same at the level cap and they could slow down or potentially stop player quality growth after a set limit (so they don't grow to be too OP for the newly promoted teams). Nordgens would have to be generated to provide replacements for player transfer.

This idea would be more difficult to implement and I'm sure there are issues to iron out but overall could be an interesting idea.