"The
Medium-Range Missile Launcher was designed by scientists at Luthien Armor Works. MRMs are dead-fire missiles that are fired more like lasers than missiles. In order to pack as many missiles as possible into one salvo, scientists removed guidance systems and made the whole package smaller. Though this was seen as a step backwards in technological development, the inexpensive and deadly MRMs have spread throughout the Draconis Combine and to many mercenary units.
The lack of a guidance system and unique nature of MRMs means that they are incompatible with special munitions and advanced guidance systems, though they can be prepared as a single-shot system."
MRMs were introduced by the Draconis Combine in 3058.
So, they're not LosTech, but they wouldn't (canonically) be around for a while yet.
Similar functionality could be had from loading LRM and SRM launchers with unguided "
dead-fire missiles" rather than the normal guided munitions (
if MWO implements
alternate ammo types in general and dead-fire missiles in particular).
As for larger launcher types for LRMs and SRMs... larger launchers would, to fit the patterns established by the other launchers in the same class, eventually become too heavy and/or bulky to be viable.
LRM-5: 2 tons, 1 critical, 24 shots per ton of ammo
LRM-10: 5 tons, 2 criticals, 12 shots per ton of ammo
LRM-15: 7 tons, 3 criticals, 8 shots per ton of ammo
LRM-20: 10 tons, 5 criticals, 6 shots per ton of ammo
SRM-2: 1 ton, 1 critical, 50 shots per ton of ammo
SRM-4: 2 tons, 1 critical, 25 shots per ton of ammo
SRM-6: 3 tons, 2 criticals, 15 shots per ton of ammo
Also, as trycksh0t pointed out, substantially upscaled launchers would kinda break the game...