okay prediction time, and I'm not going to be an asshole youtuber and make you listen to me ramble for 45 fucking minutes about this shit

AFAICT everyone will be able to use all of the new tech on all of their mechs, new and old, from day one, so I'm operating with that assumption.

Everyday staples you will definitely use:

• Light PPC - This is the middleweight filler weapon that sniper mechs currently lack. It's longer ranged than all of the variations on the ML, and even longer ranged than IS LLs and LPLs. This is a godsend to all of the mechs looking to get around the fact that X PPCs is too few, but X 1 PPCs is too many. It's huge in tabletop and will be huge here.
• Light engine - It's a Clan XL, only it weighs 75% as much as a standard instead of 50% like an XL. You will run Light engines in every IS mech and like it.
• Light Ferro-Fibrous - Not a huge gamechanger but it gives more efficiency options. It's nice to have around.

Might be cool:

• IS LBXes, UACs, and ER lasers - None of these are earthshattering, you already kind of have an idea of how they're going to work. UAC10s and ERMLs are the most likely candidates to see real play, but who knows? I couldn't have predicted that the AC5 would be as dominant as it is now.
• Light Gauss Rifle - This is not good compared to other ballistics, but it has a really goddamned long range - longer than regular gauss rifles and LRMs in tabletop. Get ready for pubbie plinking bullshit. The PRO 360 HEADSHOT crowd (and the nearly indistinguishable Helios aimbot users) will love these too.
• Heavy MG - More weight, more DPS. You already know how you're going to use this if you're going to use this.
• Heavy PPC - This is a PPC with another half-PPC taped to it. It's another possibility for upgunning a mech that can't fit another PPC but still wants to strap on a little more gun, but that 15 pinpoint damage makes me suspect PGI will nerf it somehow.
• Targeting Computers - Better filler than a BAP. You already know how these work.
• Light Active Probe - Clan streakboats save like half a ton if the range isn't too bad. Clan streakboats are kind of trash though

yeah nah this is garbage:

• Heavy Lasers - They're incredibly hot, short-ranged, high damage, and inaccurate - contrast with pulse lasers, which are hot, short-ranged, high damage, and accurate. Pubbies are going to love this trash and insist that they're OP because they do SO MUCH DAMAGE but there's really no way to make them balanced, fun, AND good without nerfing their "OP" damage and ruining their whole identity. PGI has already indicated that they're scared of making these good, so they never, ever will be. If any of them are good, it's going to be HSLs, because that's the only niche for a laser that shits out best in class damage but sucks at everything else.
• IS Streak SRMs - We already know how PGI is going to make these useless. Nobody uses cSSRMs and those are straight up better statistically.
• Light MG - Unless it turns out to be inexplicably better than regular MGs somehow, this is going in the trash. You can spare a half ton for a real MG.
• Rocket Launcher - Strictly a gimmick weapon. Fights go on much longer in MWO than TT. It might be useful if it gets more than one shot or gets super buffed damage but neither seems likely.
• Snub PPC - This is a brawling weapon that is too goddamned hot for what it does, with a secondary gimmick of doing piddling damage at sniper range. Its tabletop niche of having a huge short targeting range bracket is meaningless in MWO, and it won't displace LPLs.
• Laser AMS - This is prohibitively hot in tabletop. PGI isn't likely to fix that, because they think non-laser AMS is good and useful right now.
• Light TAG - Too short ranged to use on an LRM boat, and nobody else wants this trash. Even light mechs will be willing to pay a half ton to be safer while spotting.
• ER Micros and Micro PLs - It's like half a small laser, with even worse range. Probably not ever useful.

who the fuck knows:

• RAC2 and 5 - It all comes down to DPS, ammo consumption, and jam rates. For the record, these are not super great in TT.
• Heavy Gauss Rifles - They do a LOT of damage at short range, at the cost of being suicidally dangerous to use and doing moderate damage at longer ranges (while exhausting their precious ammo). I don't think these will replace AC20s, but they might, depending on how prone to exploding they are and how ammo shakes out. (Remember how good AC20s were, despite the falloff, back when their max range was triple their optimal?)
• ATMs - These sound like LRMs that you can brawl with, only they suck as LRMs. I don't have high hopes but this is sufficiently vague that it could land anywhere on the balance scale.
• MRMs - These are also garbage in TT, but might be cool as a midrange-ish brawling weapon if the spread isn't too bad. Problem is, the spread is canonically terrible in tabletop so I'm not super hopeful.
• Stealth armor - This is going to be great for fucking with pubbies, but in canon it's restricted to very, very few mechs and it's hot as balls. It could be a gamechanger as long as it's not too hot and there's a good mech that can fit it and there's no obvious easy counter to it - none of those is a guarantee.