What do you mean by cold fusion?
Cold fusion as I understand it, is something like muon-catalyzed or laser-hydrogen triggered fusion without the fission reaction to kick-start current thermonuclear reactions.
For now the key issue of cold fusion is being able to do it without a titanic amount of energy input to overcome the strong nuclear forces to allow fusion to take place. Without fissionables, the assembly would be much more difficult to track and depending on the process, much cheaper to build etc.
As to what's next in nuclear high-explosives- you gotta ask- to do what?
Vaporize Apophis when it swings by in 2026 threatening K-T/Chicxulub part II?
Give folks a mini-nuke grenade-size that could vaporize a city block as RAH described in Starship Troopers?
If it's the former, that's something that I imagine would only happen with lots of international involvement for the direst threats only.
If it's the latter, the key factors are cost, worry about the consequences,
and whether it's just as dangerous to the user as the target.
There's been tactical-level thermonukes since the 1950's, mines, missiles, and artillery shells. The big problem is, sure you get a big bang, but it leaves a scorched, radioactive mess. Even airbursts and "clean" fusion or EHR (neutron) weapons have some fallout. Also, let's see, you have this "special" artillery shell which is 50X as effective as a convetional 155mm howitzer shell but costs 1500X as much even with economies of scale and every cost reduction. Plus, if you have a decent enough yield, (25kt+) your effective effective range and radius of effect are a pretty close run or cause as many problems to friendlies as hostiles.