Money aside, I would still choose a TBM over any piston twin.
I've done a fair bit of IFR flying around Europe and my view now is that just having a "tank" capable of boring a hole through any weather, simply because it has boots and heated props and a heated front window panel, and hopefully radar as well, is not the way forward.
The way forward is to fly high up, above most "organised" IMC.
Pistons can do that - any half decent turbo job can do FL240 - but you are rapidly into fairly inconvenient (for passengers, anyway) oxygen arrangements, so this leads to pressurisation, and there are very few options for that. The PA46 is the only one currently in production, the other pressurised singles are all variously old wrecks, and pressurised piston twins are also all finished (Baron maybe?).
That's why a piston twin would not feature on my list. Not because I would have to re-do all my paperwork, which I would, but because - short of a 421 type plane which guzzles avgas by the barrel - it would not deliver pleasant flights.
This summer has
exposed this stuff more than any I remember. FL200 in a TB20 is right at the very top of what is possible. Yet this is as much as any non-turbo twin will do.
The real way forward in mission capability is not a 2nd motor, but pressurisation and a FL250+ ceiling, and radar.
That's why the only meaningful upgrade from say a TB20 is a Jetprop ($1.2M for a reasonable one), not a Seneca or similar, and not even a turbo Seneca.
Statistically, a single PT6 engined plane is much less likely to go down than a piston twin. Emotionally, this is hard to swallow, and impossible to swallow for the regulators (who demand 2 motors for PT, yet ban a single PT6 for the same job), but the numbers are very hard to argue with.