Disclaimer: This is just a theoretical discussion. Obviously SC2 is not in development anymore.
Lets say that the swarm host was redesigned in a way that made them more similar to carriers and also much more tanky.
-Swarm hosts have locusts that spawn like interceptors. While burrowed swarm hosts would spawn locusts that attack anything within a range of 9.
-Locusts can attack air and ground
-Swarm hosts had their size, health, and locust damage doubled and are now armored units that start with 1 armor. Requires burrow to attack.
-Their model appearance has also been updated to look more armored.
-Swarm hosts have also had their speed reduced by 25%.
-Swarm hosts cost 350/250 minerals.
-They require a hive and a swarm host nest to build. Swarm host nests cost 200/200 to build.
-Swarm hosts come with burrow by default now.
-Locusts cost 5 minerals to produce. 5 instead of 10 because its a ground unit.
Alternatively maybe this is an upgrade for normal swarm hosts instead of a full unit replacement.