Soulver 2.7.1 did support pressure, electricity for sure. Would love to have those back too! In the meantime, you can "piggyback" some existing units. For example, here is how I do my pressure conversions:

I could use volts (V), amps (A), and ohms (Ω), personally.

Something akin to the functionality of Insect would be amazing https://github.com/sharkdp/insect

GNU Units has even more units too! https://www.gnu.org/software/units/

I'm really looking forward to have the possibility to define new units from a combination of other ones. Any unit will be possible from a very limited set of basic ones.

I don't know how your unit code works, but there are only seven base units and all of the others are just combinations of them. It would be an awesome feature, even if derived units had to be added by end users.

I think the possibilities are too numerous for all programmed but the idea of ​​letting us edit our own unit of measure is just great. In fact, with this option I buy immediately!