From Richard Hadrells excellent SCCU site it appears that the effect of leaving the bands unchanged would be something like this, in the SCCU at least.
U100
Between 90 and 100% of current players would be ineligible.
Comptetition defunct, unless completely new teams can be raised from somewhere.
U125
The vast majority of current players would be ineligible but players previously in the U100 would be available. However, the U100 is currently 12 boards vs 16 for U125, presumably because of difficulties in raising larger teams.
So the best case scenario is that teams currently struggeling to get enough players will fold, worst case scenario is that all teams will do so (maybe due to lack of opponents

)and the competition cease to to exist.
U150
About half the current players would become ineligible but as there would be a vast pool of former U125 & U100 players to choose from I expect the U150 would flourish.
U175
Somewhere between a quarter and a third of players would be restricted to the Open team, but again there would be recruits from former U150 players no longer available for that team, so presumably the U175 would be OK
OPEN
Presumably largely unaffected.
To me it seems likely that the loosers will be players currently playing for U175 or U150 teams who will no longer be eligible to do so but also are not able to get into the team above and anyone playing for a U100 or U125 team which is no longer viable and therefore folds.
I also find some of the comments from the MCCU captains confusing,
For example:
I am absolutely clear that the present easily understood limits should be retained for the time being. The competitions have been running successfully under this regime for many seasons now and whilst the grading may have altered, now is not the time to start tinkering with a system that is known by all.
Sorry, what does he want to do? The statment is an oxymoron.
Leaving the nominal bands in place when average grades are increased by 20 is a major change, which certainly qualify as tinkering. If he wants to leave a system that is "known by all" in place then, surely, the bands have to be adjusted so roughly the same players qaulify?
Several of the other comments appear to be in the same vein, advocating caution or no change, whilst at the same time being in favour of disqualifying between a quarter and all of their current players (based on the SCCU numbers, depending on which team they captain, and assuming it's not an open team).
Have they actually consulted their players, in particular those who will be left without a team?