Must admit I'd forgotten all about the RTR option (another TLA!!).
For the OP the Aspirational contracts are either full month on, then month off with one recency trip (58%), or two on one off with a recency trip (72%) - those contracts are certainly being investigated/taken up by some of the higher end tax payers, hence my comment.
Once your application for PTWK is accepted, it is a permanent change to your contract, and I doubt it would be possible to return to full time working??
That's certainly true for the Aspirational contracts, but out of interest does that also apply to "Right to Request", e.g. Can a right to request worker demand to return to full time working once dependant child has left home?