A new custom firmware has been released for the PSVita this release only supports 3.60 firmware:

HENkaku Ensō is the evolution of the HENkaku jailbreak that opened the PS Vita and PSTV to a new universe of customization and user created content. Install it once and your Vita will be permanently hacked--no need to apply it after each reboot. Just enable HENkaku, install the following vpk, launch it, and follow the on-screen instructions.

Does this work with firmware 3.61/3.63/3.65? No.
How do I use this "vpk"? You need to install HENkaku first. Then open up molecularShell and press "Start" to enable the FTP server. Then connect using a FTP client and copy the vpk to "ux0:/data". On your Vita, browse to "ux0:/data" and select the vpk to install it. Then you should have a new bubble in LiveArea which you can launch to install ensō.

More info https://enso.henkaku.xyz/