The 1.5 PEM uses stronger IGBTs (different type than the 2.0 / 2.5 er PEMs and there are smaller differences too: 2.0 PEM, 2.5 PEM and universal PEM for 2.x) and the layout is much different too.
A PEM replacement (completely overworked PEM) won't show up imo since it's more or less standard electronics (typical inverter electronic circuit which is also used as a rectifier when charging) - 1.5 uses part of the motor coil when charging, 2.x not! and the "heart" is not the PEM but the circuit boards in the front which contain the software. PEM is digitally controlled since in the beginning of the development the first prototype was analogically controlled and sometimes the electronics just went crazy leaving the car not drivable at all.
A stronger car (stronger motor e.g.) would demand a complete new layout of the PEM and battery too and therefore a new software... That won't happen; we are right now maybe 2000 Roadster drivers left and maybe 500 might be interested in such an upgrade... that's a no brainer that development and production costs would cause an immense price for it. For that money I would rather go for the new Roadster
The most common failure we see is the insulation between the IGBTs and the cooling plates deteriorating and therefore getting shorts between the electric parts and the PEM chassis. There are several companies meanwhile dealing with that issue and it's a typical electronics repair job which needs some hand skills and some (basic) electronic knowledge. But it's not rocket science at all!
There are two main types of replacement for the insulation: ceramic stripes (had them, one got broken and heavy damage - blown IGBTs - was the result 4.5k Euro repair) and insulation stripes (foil, which I use now) with slightly better heat transfer ability than the original material (I would go for that...). A replacement PEM directly from Tesla still uses the original type of insulation and therefore the problem still might occur.
Proactive revision to a new insulation makes sense because it will cost you much less than replacing blown IGBTs.... (been there...)
There are some issues with the 1.5er batteries cause the connections are rivets and not welded like the later 2.x. Those rivets might get loose over time and therefore you will get bad connections inside a sheet...
I have been told just this week by my SEC in Frankfurt Germany that there is now a replacement battery (not the 3.0 but an revised 2.0) for 16k Euro incl. labour which sounds a fair price to me...
Like Gruber there are several companies now taking sheets apart and doing excellent repairs if for example a cell gets bad, so this is an alternative choice to go for...
Other parts on the roadster are down to earth and some can even be replaced with Lotus parts (mirrors, brakes).
Suspension can be overworked by Bilstein. A new set from Tesla is hard to get meanwhile!
Other parts are still obtainable. So I wouldn't worry too much...
What makes me worry though is body parts since there is the rumor that the storage in the Netherlands will be emptied up this year... And besides smaller aftermarket parts like the rear lights e.g. I am not aware of a company making replacements... Meanwhile I even consider buying a broken down Roadster for having parts in stock....