instead of trying to make a "one size fits unknown" datalogger
I think the first thing would be to list all the sensor types likely to be hooked to this datalogger and from that determine what input conditionning will be required at minimum for more kinds of sensors
so at least it's known which input conditionning facilities should be on a standard datalogger and which type can be left off a add-on adapter board
also someone should do an inventory of all open source datalogger project that can be found and enumarate their features and scan them for "good ideas" to incorporate in this design
datalogger are often needed but they come in so many brands and model and industries because the people who measure temperatures over weeks don't know about the people who measure fuel/oxygen ratios during minutes and they don't know about the people who measure viscosity over months but they can all benefits from a single common datalogging core with just add-on for their specific application
datalogging for most is an expensive and R&D intensive affair that has no re-use value that's why people pay 500/1000/2000$ for a datalogger that have specs all over the place and there's a reason for that , there's big money to be made in keeping each project unique and personnalised and impossible to compare/shop around for
and lastly the most important of all, this project needs a good name that clearly indicate what it does to people who need it yet don't know what it is yet and it should be easy to find so that the next time someone needs to log the humidity of their bathroom over the next year they don't re-invent the wheel again !!!