Interfacing vs. replacing

My house has an old wired alarm system, probably from the 90s.  It has three 770-A Simplex "Security Command" keypads, and a box which probably contains a DMP model 1912 board.  An additional Honeywell box provides cellular connectivity (voice only).

I could probably throw everything out and use konnected boards + tablets.  The keypads use a 4-wire interface, which I could use to power the tablets.  But I'd like to save the existing setup for two reasons.  1. it keeps running during power outages; 2. it also interfaces to a couple of smoke detectors.

Additionally, I am a Google Fi subscriber and can use data-only SIMs very inexpensively.  So I would like to connect to the internet via LTE, again to keep operating during local outages.

I am wondering if Konnected has a solution that works for me.