Its all about a lack of cash flow, selling buildings is only a relatively short term measure, grabbing the faithful's hard earned cash and controlling it is a clever idea, (not new, they have asked for this for years) how much would remain in the fund permanently ? millions ?
When the cash dries up, so will they.
I am not an expert on Charity law here in the U.K but I am aware that shifting funds between charities is a doubtful area, the congregation's trustees could be in an awkward position eventually.