Furthermore, 75% is pretty terrible as a switchover point, as it guarantees that old nodes will still see a 25% forked off chain temporarily.
Yes, 75% plus a grace period is better. I prefer a grace period of about 4000 to 8000 blocks (1 to 2 months).
From my discussions with miners, I think we will be able to create a hardfork proposal that reaches about 90% support among miners, or possibly higher. I'll post a summary of those discussions in the next 24 hours.