[Brekkie]

Unfortunately I can't really seeing there being an impetus on either the public or commercial side for any further conversion to HD now. The main PSBs are in HD (and regional) and I expect that's all that really matters to the government. I can't imagine they would be willing to support another digital switchover level campaign where people have to pay to upgrade equipment they (perhaps reluctantly) paid to upgrade when analogue was switched off; especially now during a cost of living crisis.

Freeview HD / DVB-T2 support has been standard on TVs for several years now.  The longer time goes on the more households are likely to have TVs that support this standard (not including those using Sky/Virgin).  In the short-medium term retaining DVB-T on PSB1 or PSB3 would allow for a legacy SD service of the main channels for those who's TVs can't receive DVB-T2.  The other multiplex could then be converted to DVB-T2 with only variations for nations.

Exactly.   Been standard since 2016 and widely available before then, and I suspect many have upgraded since then to get the latest smart TV apps too.

It seems Sky and Virgin are finally moving to ditching SD simulcasts and being HD as standard, so Freeview can't afford to be left behind.