As for the creation of new term programs, I'd have to say making it RELY on a FOSSIL driver is a BAD idea.
The reason to use FOSSIL, and it is a sufficiently strong reason, is that with some layer of abstraction at that low level, you can't do end-to-end link encryption transparently. For example, if you want to do a download over a secure channel, if you have to use an external protocol, and if that protocol talks directly to the serial port, then you can't use it, because the protocol will see only gibberish. If, on the other had, the protocol driver uses FOSSIL, and if your FOSSIL can set up an encrypted channel, then the protocol will perform as expected without being aware that it's underlying connection is encrypted.
Almost NO new door software uses FOSSILs, because companies like Compaq are making more-compatible machines with less proprietary garbage in them.
The reason to use FOSSIL is not compatibility, but abstraction. It's the only abstraction for serial communications the PC has, and we'd better take advantage of it. Eric