The simple answer is yes.
It’s possible to encode or tunnel anything over any protocol.
The next question is why isn’t it done more?
For the above reasons it’s actually more common to see other protocols run on top of http. This is especially common to prevent blocking and censorship by making the traffic look like normal http traffic when it may actually be private messaging apps, file transfers, VPN, etc.
Not exactly what you asked for but Joplin files are markdown. The app itself (very cross platform) renders them in a nice format. https://joplinapp.org/
The addAddress call may just be configuring the local side of the VPN. It’s hard to know without looking at the rest of the code.
The general workflow when establishing a VPN connection is:
addAddress may just be part of the configuration. A very cursory search suggests that OpenVPN may be being used as the underlying VPN implementation framework (not uncommon).
You are correct, I had not noticed they did away with that icon until you mentioned it now.
“Lauren Boebert makes woman feel threatened and unsafe in the women’s bathroom.”