A possibly stupid question....

[NomDeClavier]

If a pushchair is compatible with maxi cost carseats, and comes with adapters, and there's a bassinet from a different brand that's also designed to be used with the maxi cosi car seat adapters, can you plonk bassinet from brand B onto brand A's frame?

Yes. I have done it - used the (old style) Micralite Toro carrycot on the Bug Bee using the maxi cosi adapters. It works fine - looks a bit odd because the carrycot is higher up than carrycots usually are, but works.

In theory yes, however in practice, PLEASE dont! All pushchairs are carefully safety tested and part of that process is a tipping / stability test. Putting a heavier carrycot onto a lighter frame or one where the centre of gravity is different could result in disaster.
Your child is precious, and you would be held responsible in the event of an accident.

actually yes, there were a few hairy moments on windy days now I think back.