Note the tie to funding a tax cut. This is what caused Liberal Democrat MPs to refrain from supporting the motion. If Labour had omitted that clause, they might have been able to peel more of the rank-and-file away. LibDems in government were never going to support a tax policy which was not included in the coalition agreement, but back-benchers might have been tempted to support an unadulterated statement of LibDem policy.
There is some justification for directing the revenue to reducing the effects of inflation on benefits, for extra funding for public works - which Vince Cable appears to favour - or simply to reduce the public sector debt. Labour speakers indicated that they wanted to reintroduce the failed 10p starter rate of tax, which the IFS describes as "too complex". The coalition has already factored in a big increase in the personal income tax allowance and a 10p rate is not likely to feature in a future LibDem manifesto.
This confirms my impression that Liam Byrne was talking through his posterior last week when he spoke of raising £1.3bn from a bankers' bonus tax. Only the most fervent socialist in the House would seriously consider a tax of more than 100%.