Omg, First, search this web site, lots of ideas . But, what CAN'T you do? With a fully capable linux computer, almost any software development you'd like. Control hardware is the best part. Use those gpio pins.
Ok I admit that I am late to this game. I heard people talk about it, but I didn't understand why. But now, there are more projects than I have time.
I think that most than one idea instead of another, you need to be suggested for a path. We have no idea the point from where you start but sure if we make suggestions these are mostly based on our personal interests and feelings and matching yours is just a guess.
In my opinion, you should search digging here in the many areas where the PI is involved (from PI Challenges to the specific PI dedicated sections and more, as well as the PI-HATs and accessories) and on the projects showcased in hackster.io and the very pi raspberrypi.org site. But I think that the right path to finding the right direction is searching with a discriminating keyword: physical computing Probably this is the most intriguing and large series of interesting opportunities you can find.
I would start with the question, what is your background?
If you have little to no background in electronics or computer sciences then I suggest you start with the basic of establishing a Pi desktop. Most individuals are familiar with some kind of desktop computer. Whether it be a Microsoft Windows or Apple Mac operating system (O/S). Raspberry Pi's have a number of O/S's depending on what you may want to do.
Raspbian O/S is a good starting point. Find out how to download the image files needed. A full version of the O/S is what you need. Lite version removes all the overhead associated with a graphic user interface (GUI).
Starting at getting a desktop working gets you familiar with imaging SD cards and configuration that have been simplified through raspi-config. Work through the command line gives you exposure into computer O/S details. Desktop builds give you something for your efforts in the end. You deal with conductivity to the Internet with wireline or wireless technologies so your Pi can actually use the Internet. Doing local customizations through raspi-config provides some foundation knowledge, like establishing interfaces to devices that use I2c or SPI.
I teach a one day workshop. Getting a Pi displaying content to a screen is an accomplishment. Getting internet working is the second step. Most O/S's are delivered baked. Pi O/S's give you something to explore.
