Republic uses the term handover to refer to moving calls between WiFi and cellular. I don’t believe that’s what you refer to, however, please correct me if I’m wrong about that.
I think you’re referring to the fact it often takes longer (days as opposed to hours) to transfer (port) Republic numbers due to their classification as landlines (wireline is the more correct industry term). For the purpose of porting, Republic (and all VoIP) numbers are indeed classified as landlines.
That said, there’s no reason for loss of service while waiting for one’s number to port. Current service (Republic or otherwise) continues until the new provider competes the port (however long it takes them to do so).
I’ve seen no announcement from Republic that suggests there is any intention of mass porting 200,000 Republic numbers at once. Republic has stated details regarding new plans will be forthcoming in December. At that point, current members will have the option of moving to the new plans. Only if they make that choice would it be necessary for Republic to move their number and we also don’t yet know the details of how that will work.
Generally, I don’t hear from many who think Google Fi’s pricing is particularly competitive. Fi’s got some good features for international travel but its plan pricing is nothing special.
Spectrum Mobile, like other cable providers, generally reserves its best pricing for those bundling Internet and/or TV with them. This can be a good deal if one is interested in bundling but not so much if one is not so inclined.