Both my road bike and the wife’s are the ‘old’ 130mm rear axle spacing (and QR).

If I wanted to stick a more modern droupset on the wife’s bike to replace an early SRAM Rival 10 sp set up, I assume I am quite limited now as everything has gone 135mm?

Rim brake road bikes are still 130mm

If it’s steel you can probably make a 135mm hub fit.

Rim brake road bikes are still 130mm

Didn’t know that!

can they run 12/13 speed though, is there enough space?

If it’s steel you can probably make a 135mm hub fit.

Carbon…

can they run 12/13 speed though, is there enough space?

Yes, but that would involve not running Shimano so no idea why you’d want to 🙂

You might need a new rear hub but 11 speed/130mm hubs have been available for quite a while now.

Alternatively you could opt for 4700 series Tiagra which is still 10 speed but uses current shimano cable pull ratios.
Another option is 105 or ultegra with an 11-34t cassette, these are available with the largest sprocket overhanging the FH body, like 11 speed MTB groups use, thus allowing backwards compatibility with 8/9/10 speed FH bodies. So there are at least two simple(ish) ways to avoid the need to change the rear hub/wheel.

Yes, but that would involve not running Shimano so no idea why you’d want to

I don’t have any idea how many gears modern groupsets have now – our MTBs are 9sp and our road bikes are 10 sp (which was super new when we bought them).

Current Ultegra “only” goes up to 11. That’s what I’m using on my 130mm rim braked road bike.

Does an 11sp cassette need a wider freehub body or will it just fit on a 10sp freehub body?

Does an 11sp cassette need a wider freehub body or will it just fit on a 10sp freehub body?

Yes, unless it is a shimano 11/34 11spd which will fit on a 10spd freehub.

I don’t have any idea how many gears modern groupsets have now

Shimano 11, Sram 12, Rotor 13.