I'm gonna get the crap kicked out of me for this... but here goes.
If you want a new computer that runs modern apps at a reasonable speed... buy an A1, or a PC, or an Apple Mac. They will trounce even the most powerful 'real' Amiga when it comes to raw computational power.
If you want to play old Amiga games and apps... use your existing Amiga if you have one, or buy an Amiga 1200/4000 second hand. Or even see above and buy an emulator for it (it works to some degree at least).
If the A1 were to have an A1200 board attached (which it won't anyway), it's still TWO seperate computers. If the A1 had the old custom chipset built on to the motherboard, probably using 68k emulation... it's not a 'real' Amiga, so you wouldn't be happy! If it had a 68k chip AND custom chips on the motherboard, running exactly as real Amiga hardware does... you might as well have bought an A1200/4000 anyway. At least they are expandable, where the A1 version wouldn't be.
Why doesn't somebody resurrect the Siamese system? It had the makings of an excellent project. I couldn't get the serial version working, and at the time I hadn't got a PCMCIA network card for the miggy. But surely that provides a partial solution to the problem of adding a classic Amiga to the A1?
Ok... just to prove I have a sense of humour, I'm going to bash myself!