I give it even money if we see ER medium, ER Small, Streak 4 and Streak 6 in 10 years. Similar for the rest of the A/C families. You can bet that SLDF King Crab drivers looked at those Hermes punks with their spiffy new Ultra A/C 5's and asked, "Why can't I have Ultras?" That's not a case of needing the Clans to push innovation. That's just a matter of "we haven't figured it out yet."
Other's have said that mechs, especially the heavy cav role, won't be quite as fast. I agree that most of the weight savings would go into weapons. Everyone had gotten along just fine without maxed armor on everything for centuries. The 3050 crop would see a lot more firepower, but not much change in armor levels. So a lot of mechs are going to die, pretty quickly. But then I expect development to kind of mirror the main timeline. Designers will start to explore other corners of the iron triangle. Eventually we have a swing back to SFE's, like in TRO3060.
C3 would never have taken off. It was almost exclusive to DCMS for a long time, even with the Outreach agreement. But the only reason the DCMS used it was because they were at a disadvantage against the Clanners. In a "fair" fight against AFFC units, few if any samurai would "stoop" to using C3.
Technologies we would not see are light gauss, and heavy/light PPC. Okay, maybe the light PPC might show up, if that's an outgrowth of the snubbie, which was developed back during the Star League. The hPPC was a direct answer to the ruinous cERPPC, and the light gauss was an attempt to match the Clan gauss. I'm not sure about HGR and iHGR. Light engines probably wouldn't happen, and neither would heavy or light ferro fiberous.