But the only logical reason for using the international platforms for main line trains is to make use of their additional length. If you don't want/need that extra length, then there is no point whatsoever in building the necessary flyover to switch sides on the approach, you just move the normal platform allocations to the left (looking into the station), by putting four or five platforms worth of the Windsor side into the former international station and any extra long distance services then run into the middle of the station. They already have a plan to allow for this increase (if Crossrail 2 doesn't render it obsolete), with a single bi-directional extra line from Surbiton to Clapham Jn, so there's no need for a new line from Woking.
However if the DfT's priority remains to provide such and such an absolute number of seats on the overall route, I'm afraid there's no way they'll revert to 2+2 seating on Portsmouth trains. They won't want the massive criticism - and in any case, Portsmouth is no special case - they use the same basic trains on runs from Euston to Crewe.