Yup, when it comes to Multiplan we still require the original cartridge - OR - the UberGROM version << HERE >> which you might want to check out. I've never bothered to try it since I already have two Multiplan cartridges and have no use for TI LOGO or TI LOGO II which are also part of the .BIN image. Maybe with luck, "someday", in the distant future, we might get lucky and get a variant of the FR99 that supports GROM capability, however I'm not holding my breath.
As for BA-Writer 80, I love it and use it too. The way it's designed though, it has multiple programs/entry points, BUT it would still be cool if the main module could be converted to FR99 use just for faster initial loading (hint), even though both programs would still be required on the diskette.
I'm not sure if you know this or not, but there is an alternative to the original FlashROM cartridge case made by Atari Age user LCD with a slightly smaller profile. You might want to see the replies in my blog entry on it << HERE >> for photos. If you PM the guy he might make one for you.
I have have no clue when it will be ready, but Ksarul is working on a Myarc DDCC-1 clone that is DSDD 80 track capable of addressing four 2880 sector (720K) diskettes for a total of 2.88 megabytes of storage, which would only require two HxC's and get you partly compatible with your system in Manila.
The Atari users have a emulated "hard drive" using the Lotharek, but I *BELIEVE* that to do something like this on the TI would require either modification of the DSR on the FDC or possibly (guessing here) an UberGROM with some sort of DOS integrated into it's design, which is probably never going to happen. I suppose it *MIGHT* also be possible to hack and insert a second FDC into the TI using a different DSR header other than the >1100 which the TI now uses. In the end though, it would probably be easier to start from scratch and make an FPGA based SSHD to plug into the P-Box that uses an SD card. If that ever happens, it'll probably be years away.
For quick and dirty text files, you could also try the EAII80Edit-8.bin image for the FR99 << HERE >> as it's 80 columns. I find it VERY useful for editing my FAVS file for Stuart's Internet browser.
The Nano-PEB.... yeah, sigh. I feel your pain!