As 3GPP announced a new milestone on 5G release 15 standardization, that is completion of Stand Alone mode specification of 5G operation. The big question arises, would there be a split in 5G deployments in near future (i.e. with the availability of equipment's and mobile terminals)? because there is no obstruction possible on NSA mode rather NSA is going to have a major coverage, in fact for large coverage areas NSA would be there and probably SA would cover smaller coverage areas through small cells.
SA mode is about no LTE for control plane but both plane would be on NR only. So SA will put LTE on spare, really? That is feasible only for smallcell deployment cases as the operators are not going to make LTE spare due to heavy investment. Rather that is the upbring of 5G in real sense. We have already witnessed gigabit LTE deployments and vested interest of operator on it through LAA and LWA due to LTE based carrier aggregation CA or multi RAT convergence.
That trends is leading towards the solid root for NSA mode, SA mode would be filling the gap and caveats but not overshadowing it anywhere. The Fixed broadband uses case of 5G NR so far has been for millimeter waves but sub 6 Ghz NR has yet to come for mobile use cases ( as we all are waiting for mobile terminals use cases).
LTE is far established and well coordinated for network spread and coverage enhancements, 5G NR has yet to come for that level of maturity and that's gonna take long time. Still LTE and 5G both seems to be moving parallel as there seems to be no obstruction for LTE as well. Technology has matured and taken its much advance form in LTE adv pro. In fact LTE adv pro is well taken to accomplish much of 5G use cases, whether it be massiv IOT, V2X or URLLC use cases like for robotics or healthcare.
Therefore 5G is not about 5G NR only, There is much more wider outlook for 5G, like Network Slicing, Application defined etc, etc. 5G is a big hash, technology under which create a comprehensive system, not a isolated sliver.