Looks as if the Moto E 2nd gen phone my very elderly mother-in-law has on Tello will continue to work on Tello for some time, unless the battery gives way. I guess you could say, getting a new $30 phone with 4G LTE + VoLTE that is still going strong several years later, is an enduring benefit from the R+ days.
My thinking is that since all CDMA phones have GSM radios, it is possible to use a GSM SIMcard in a CDMA phone. Long ago, there was a SlickDeals thread about using a FreedomPop GSM SIMcard in the Moto E 2nd gen phone that you mention above.
Not sure, but from what Tello said, it seems the key to transitioning the a Moto E 2 to Timo is VoLTE support, which is necessary along with having the necessary GSM bands. The 4 G LTE version of the Moto E 2 was a bit ahead of its time for a budget smartphone it seems. My concern is how long the battery will last and how easy is it to replace.