This really really depends on how they implement Community Warfare. The devs have stated they will not be working on implementing the clans until after that goes in. There are questions that will need answering before I could feel that anyones opinion was sufficiently informed to constitute more than a gut reaction.
- Who gets to join the Clans?
- If anyone can align with the Clans and get shiny overpowered Clan mechs (omni or otherwise!), what incentives will there be for new players to align themself with an Inner Sphere faction?
- How will Clan forces be matched against other Clan forces and against Inner Sphere forces?
- Will Community Warfare create an environment in which players can find matches at whatever technology level (IS T1, IS T2 or clan) they prefer?
Clan tech will almost certainly accelerate gameplay in matches where it is involved. Increased ranges, combined with higher heat dissipation and lighter/more powerful weapons makes for a pretty massive increase in kill power, while improved XL engines and ferro-fibrous/endo-steel technologies make for relatively small increases in actual survivability. On the other hand, the Clans won't get any super pilots advantage (as in the tabletop game) because it's real people piloting those mechs.
I suspect that a tonnage ratio of 5:8 would probably balance out the enhanced speed and firepower of Clan mechs against Inner Sphere mechs that are fully customised with the full range of tier 2 equipment. That ratio is close to the unofficial consensus value for tournament play (balanced on tonnage rather than BV here in Australia) in the tabletop game. Excuse me if I don't provide an exact source on that though! MWO may not balance similarly, but I'm expecting it will.
The trick (as always!) will be to decide whether to make the Clans have the same number of mechs with lighter tonnages or make the Clans have less mechs at the same tonnages. Either method has it's issues.
The same number of mechs, but with lighter tonnages plays to the Clans advantages. The Speed and Firepower of Clan Assault mechs are only a bit above that on InnerSphere Assault mechs. The Speed and Firepower of their Lights and Mediums is far above that of InnerSphere Lights and Mediums! In general, it would be like fighting 8 super Jenners in every game. They would tend to easily outmanouever any Inner Sphere force.
A lower number of mechs, but in similar weight classes means that each individual clanner is more valuable to their team. Killing just one knocks out more of their firepower, but each Clanner could reasonably expect to beat any single Inner Sphere mech hands down. It would be like fighting 5 super GaussCats in every game. The Inner Sphere would gain a slight strategic advantage, but would have to work together well to avoid being absolutely destroyed one-on-one.