A few points:
As far as I can recall, the motive behind McCreevy move towards individualisation was to boost the labour supply, by reducing the MTR faced by the SAHM, who was thinking of entering the lab market.
I take no position on whether we should force/encourage SAHM out of the home and into employment.
I recognise fully the invaluable work done by SAHM in the home.
At the moment, the tax system can mean that if two people marry, their tax bill on their combined income will fall.
Example: Bill 40k married Jane nil income, Bill's SRCOP will rise from 32,800 to 41,800, as some of the tax band is transferable. Result = lower tax compared to single
Example: John on 40k marries Mary on 20k - AFAIK here the tax bill will fall again.
What I suggest is full individualisation, which may be portrayed as anti-SAHM, combined with child tax credits to reflect the valuable work done in the home by the SAHM.
This would mean that on marriage, income tax wouldn't change.
Tricky policy though, my mind isn't totally made up, either.