I have been researching the internal workings of Commodore 64 GEOS and GEOS128. While (barely) usable without, these two operating systems shine when used with a RAM Expansion Unit (REU.) The difference between the REU and the SAMS is the REU offers DMA capability to transfer chunks of memory (including the entire 64k memory map) into 64k banks on the REU, no CPU required.
Even so, while I should be doing other things, the glittery squirrelTM of always wanting GEOS or similar on the TI has attracted me right now and I believe it to be fully feasible to port GEOS to the TI. Obviously, the binaries will not be compatible as the 64 and 128 are 6510 and 8501 CPU (respectively,) neither will the disk formats as GEOS uses a custom filesystem on top of CBM DOS and the GCR low-level format, but I expect to be compatible with the data files (geoWrite, geoPaint, etc.) with transfer possible via the Converter tool.
I have been playing with using the 1571 to read 180k (SSDD) TI disks to make it easier to move files back-and-forth. The 1571 cannot be used to read 90k (SSSD) TI disks as the 1770/1772 in the 1571 is locked to the DD MFM mode by grounding the density select pin. I think a modification of connecting the density select pin to an unused pin on the 6526/8521 on the board can be used to over-come this limitation, but right now I see neither the necessity nor the practicality.
Back on-topic: ergo, I will have to pick up one of these, as well.