I think this might be patent-dependent. Unless it's owned by HP then it's unlikely that it could be distributed as a part of webOS, it could extracted from a 1.4.5 doctor or downloadable. I imagine webOS 2.x and 3.x could be modified to make it work over all devices though
I believe the Classic source is now HP property. The PalmOS ROM image however is another story altogether, since PalmSource and PalmOS was bought by Access. Palm, however, did purchase a perpetual Garnet license so that may count for something... or not.
Like you said though, the image can be easily extracted so that wont have to be distributed or hosted separately for download. The work lies in updating Classic itself. Hopefully HP will see to it in the coming months.
Supposedly the source was given to Palm. It would be pretty cool to see Classic running in HD mode on the Touchpad. Possible? There were multiple resolutions for PalmOS. Throw in accelerometer support...
Visor Deluxe->Visor Prism/Digital Link->Treo 650->Treo 700p->Pre->GSM Unlocked Pre 2 (wifi only)->FrankenPre + Touchpad 32 ->+ Touchpad 4G ATT + ATT Pre3 + 64 White Touchpad... bliss.