I think one reason for the backtracking is to do with the "real time information" system they were hoping to be in place simply won't be. The whole removal of CB for HR taxpayers is going to rely on people letting HMRC know that they are HR taxpayers, because the government's systems aren't clever enough to do that yet. The idea is that they will be, soon, but who knows?
As for how much is "enough" money - it all depends, doesn't it? Great if you managed to buy before the house price rises and so you have a nice small mortgage. We didn't. We have a 3 bed semi and a mortgage of nearly £1400 a month. Ok, we didn't have to buy. But I don't see some of the posters acknowledging on here that one reason they don't have to work is because they were lucky enough to buy a house early enough.
And there is a big advantage to a universal credit scheme, ie low admin costs. What's the point in bringing in a means tested system that costs as much to run as the savings it generates?
Like I said, I can't see how they are going to do this until real time info properly works, and they know how much a " household" earn.
Final point - if this does come in, and you / your DP is only just over the threshold, the solution is to increase pension conts to get you just under the limit. The government have said pension conts will not be included in gross pay amounts.