I suppose using the Klondike Prototype Clan weapons would be possible. Currant IS weapons equaled early Clan weapons so I don't know why the prototypes couldn't also. But you'd only see them for a limited period of time.
I personally am fond of Lingonberry IS weapons, but to each their own. Inferior prototypes that are quickly rendered completely obsolete is not at all the type of thing I was illustrating. I don't know whether the trans-ER example stats I gave work for this, so I apologise if they're either overpowered or underpowered, and for clarification the intent is a tech upgrade that can swap right in without issues, or at least with only modest issues- a way to roll out new technology in a "drop-in" form. For most new weapons tech, the game stats
allow the interpretation that you can relatively smoothly roll out new technology by simply buying or producing a component and slipping it in as a field refit: swapping out an SRM-6 for a Streak-4 or NARC launcher, swapping an AC/5 for a Rotary AC/2, or an AC/10 for a Light Gauss Rifle, and in the vast majority of cases it will work fine without needing to overhaul the cooling system or anything. Maybe the RAC/2 won't work well on a 'mech with heat problems, or the Streak on something with a really big magazine, but for the most part new guns and missiles are much more workable as early field refits than beam weapons- to say nothing of how easy it is to roll out new ammo types for existing weapons! Such drop-in components for upgrading or otherwise reconfiguring machines are common IRL, being the intended point of a lot of aftermarket replacement parts, so it kinda bugs me when new tech in BT looks like it should be able to take such a form but doesn't: the TR weapons are to be read as "real" ER tech, not immature prototype suff, but engineered/calibrated/whatever for a slightly different balance between performance and energy efficiency, for the specific purpose of being more suitable as a field refit, because stuff like the "upgraded" Panther 10K is just masochistic. For another example, a Trans-Pulse ML could be 1 ton, 1 crit and 3 heat to swap in for older ML and have reduced performance compared to a full-size MPL: less damage and/or only getting a -1 TN bonus instead of the full -2 bonus. Alternately, it could instead have performance that is more unique game-wise but still easily fluffable as an application of the same technology, such as a half-damage MXPL.
We do have hybrid weapons. The Cyclops Eye Laser on the Drillson Hover Tank uses PPS and Laser Technology. There are lots of other non standard items described in the fluff. Assigning Quirks to the weapons helps but there's things they don't cover, besides costs. For example, by the fluff the Parti-kill PPC can't fire at extreme or LOS range. The HellStar PPC has a greater minimum range. The Tiegart PPCs are 10% smaller and the Nightwind Large Laser is bulkier and heavier than newer lasers.
That's also nothing like what I meant to describe; like you said, unless using fractional accounting or other high-level rules, a Donal and a Hellstar are identical. Think more along the lines of the canonical Silver Bullet or, if you're more of a clan fan, ER Pulse lasers and Streak LRMs: "Hey, why don't we have this upgraded tech available here as well?" I rather like minimum ranges because I think they're an interesting mechanic, but I recognise that it's not a big enough deal for most people to feel that it justifies what is in effect just another size of Pulse Laser whose practical purpose is questionable, so I also proposed using the fact that PPC are a different technology to justify more eccentric mechanics, though I think I went more eccentric than I had to. Maybe I should focus on things whose stats I don't even need to explicate, given my tendency to drift far into whimsy?
RAC are based on LAC, so I've long wanted a second-gen "Heavy RAC" based on standard AC.
Kinda similarly, I like the idea of a Light LB-X where the LAC range penalty and XAC range upgrade simply cancel out exactly.
I'd love to see a Silver Bullet LGR, because it makes perfect sense to me. [drool]
Light and Heavy versions of the ER PPC and Snubbie would suffer a bit from the rounding conventions, but still be useful and cool. (and IMO that slight nerf would improve their balance since the canon PPC variants are, again IMO, at least a bit overpowered)
How about a Fusion version of the Heavy Flamer? For that matter, how about an ER Heavy Flamer?
This is all about style and not about function, but I would like to have Inferno Rocket Launchers and Incendiary MRMs.
'Mech Mortars in SRM range bands, with double-size payloads? "'Mech Grenade Launchers?" "SRMortars?"
Heat Ray Lasers: purpose-wise roughly analogous to Infernos and Plasma Cannon, fluff-wise similar to Re-Engineered Lasers
For clan stuff, I can get behind Chemical Heavy Lasers.
I'm kinda on the fence about clan Light Gauss and/or Silver Bullet because I rather like them both as things Spheroids get that clanners don't. >:D
Heavy Pulse Lasers would make a sick sort of sense to me: address the concerns that led to Improved Heavy, while "fixing" the unglamorous "skill-minimising" nature of Pulse weapons.