IMO, Phlebotinum/Explodium/Handwavium should be kept out.
Here's a good
link to a website full of cool real-science future weapon ideas.
Basically, here's what I think further progression should be like:
Lasers & Directed Energy:
Lasers develop from regular Pulsed Lasers into Free Electron Lasers, and then Phased Array Lasers. X-Ray/Gamma Ray Lasers can also be added, but I don't know how well they'd work in a terrestrial setting.
All lasers would have Electrolaser variants that are devastatingly effective against cyborgs, somewhat less effective against tanks and ships and ineffective against hovers, and unable to attack airborne jump cyborgs and VTOLs. Electrolasers would do equal damage to normal lasers but would have better damage multipliers against cyborgs, tanks and ships and a slight disabling effect, but they would be heavier and more expensive. X-Ray/Gamma Lasers wouldn't need an Electrolaser variant since they can screw electronics on their own.
Lasers would generally get better in raw damage output with higher tech. The Stormbringer anti-aircraft pulsed laser would continue on as a dedicated air-defense laser weapon.
As for the existing Plasma Cannon and EMP weapons... meh. The above stuff described leaves off from the Pulse Laser and follows the Flashlight/PulseLaser philosophy instead of the confused HeavyLaser/PlasmaCan/EMPCan nonsense. As far as I care, they could just be removed. The Heavy Laser and Plasma Cannon have pretty good PIEs which can be recycled for the FE Laser and Electrolaser, though. The EMP Cannon PIE is just plain fugly.
Mass Drivers & Hypervelocity Kinetic-Kill:
Well, we've already hopped and skipped through RailGuns in the existing game and end off with Gauss Cannons. I'd go further by developing Gatling Gauss Cannons, by applying the tried-&-tested philosophy of Moar Dakka to increase ROF at a slight cost of accuracy. Further developments would be even-more-amazingly-dense anti-tank slugs, hypervelocity fragmentation rounds that can scrag large groups of cyborgs or VTOLs, and scramjet-assisted homing slugs for extra awesomeness.
Offshoot weapons of this technology branch would be very high-tech anti-aircraft defenses firing those scramjet-assisted homing hypervelocity fragmentation slugs, and of course, various artillery weapons.
Mass drivers would generally get better in damage and ROF with higher tech.
Missiles & Explosive Warheads
Missiles have a hard time here. The current warheads used in reality is the tandem High Explosive Anti-Tank(HEAT) shaped charge, which creates a focussed blade of liquified metal using a conventional explosive, which can cut through steel like a (very)hot knife through slightly melted butter. In Warzone, the Scourge Missile seems to use a very low-yield nuclear explosive to generate it's shaped metal jet(thus not making it an er... "actual" nuke).
Apart from using bigger nukes(which is a no-no for the Project), the only way ahead from here seems to be nano-gimmickery and antimatter. My idea for an extremely high-tech missile warhead would be for a small nuclear warhead to drive a shaped-charge jet of a specially-engineered nanomaterial, containing some kind of antimatter-containment nanoparticle(say for example, an antiproton stored inside a fullerene) that loses containment under the extreme heat and pressure it faces in the shaped-charge jet, leading to an annihilation reaction that would...
It would be a really, really high-tech weapon. If combined with a mass-driver as a launcher and scramjet propulsion, it could be a very, very expensive, very long-ranged, very accurate, and very, very powerful weapon with moderate ROF(whew, that a lot of 'very's). It would of course be counterbalanced with low durability(justified, there's antimatter on board).
The generic 'bigger warheads', 'more missiles', and 'more range' is just boring compared to zany engineering.
![Razz :P](./images/smilies/icon_razz.gif)
The above idea also borders on the edge of Applied Phlebotinum, because even if you do store antiprotons inside fullerenes, they might just quantum-tunnel through the electron cloud, blast some nucleus and cause the entire molecule to fall apart in the ensuing carnage. And that's not considering how hard it would be create so many antiprotons, and then store them inside nanoparticles of regular matter. Of course, a conventional magnetic bottle could also be used to store antimatter, but I don't like the notion of having to constantly waste energy just to prevent your own bomb from exploding in your own face.
That wore me out, so I think I won't be talking about futuristic flame weapons, armor, active defenses, stealth, or anything else related to this until tomorrow.