Ideas I've had over the years that could pan out and be useful:

SMS-DB: Stands for SMS-Data Burst. Used to allow those with low cell signal or no data plan to transfer data between a phone and some client via the standard SMS text space. Would be slow, but would act kinda like dial-up over SMS (as mobile lines are compressed on all service levels, even LTE, so traditional dial-up wouldn't work!) I have a general idea on how packets would be laid out, but that's about it so far...

everything2PNG: Allows one to transpose any file's data into a PNG with a 3 byte per pixel (full color RGB), which allows for a "compression" of sorts (about 91, 93% on preliminary tests) AND allowing further, more efficient compression of the resulting file. (Plus... it's just kinda cool to see files transposed as PNGs.) I actually have a simple transposer to go to PNG, but can't yet go back. Large files (around 600MB) use upwards of 4GB with efficient paging and other optimizations via NumPy so far, so it's not *viable* yet, but it's coming along nicely.

RPi-GPIO Interconnection Bus: A master/slave or round robin method to allow for Raspberry Pis to communicate using GPIO, which can help free up network bandwidth in RPi cloud computing clusters. At most, this'd allow for 4 bits used for pushing to the GPIO "bus", and 4 bits used for pulling from the "bus". 8 pins total are usually unused minimum, so either 3 or 4 pins for upload, 3 or 4 for download, and potentially 1 or 2 for commands, general non-data communication, etc. I made a version of this concept using Round Robin for a client, but it was horribly slow. (I also don't have distribution rights for the code, so i'm working from scratch.) Definitely doable.