In Minecraft 1.16.2 Pre-Release 1, a change was made to ender pearls and other projectiles. They are now affected by bubble columns, which allows us to keep an ender pearl (or other projectile) suspended indefinitely! This inspired me to design this (somewhat) useful contraption, the Instant Recall System.

The Instant Recall System (or IRS) consists of a suspended ender pearl in an upwards bubble column and a simple hopper clock, which will cause a piston to extend and touch the ender pearl. This means that you can preprogram a time into the clock, and after that time has passed, the system will automatically teleport you back to itself. Sadly, there are several limitations to this; the clock needs to be in a loaded chunk to function. One easy way to get around that would be to build this system in the Spawn Chunks, where the world spawn is located, because these are always loaded automatically.
If you don't want to be teleported back to the spawn chunks - maybe because you've built your base far away - you can build a redstone chunk loader. These usually work by periodically shooting items back and forth through a nether portal, as every time an entity passes through a portal, it loads the other dimension for a small period of time.
Of course, the two greatest limitations of this teleport system are that you are always teleported to the place where you built the machine, and cannot use it to freely teleport. The second big limitation is the fact that there is no easy way to remote-control the contraption; you have to set a timer, and after that runs out, you will be teleported, regardless of where you are and whether you want to come back or not.

The main viable use I see for this system is for vanilla survival exploring. You can set the clock to an hour, for example, and then
explore the world for one hour, or go mining, or do something else far away from your base. Then, after the hour has passed, you don't need to travel all the way back to your home - this is especially useful if you've gotten lost!

Important Note:
I have not tested this in a very in-depth fashion, I simply built the system in creative mode and used a command to teleport thousands of blocks away. Everything should work, but if you find a flaw in the system, please tell me about it, and I will try to fix it!