I want to hear what people think it WILL be like, fighting on the way in. What planets between the edge of the empire, and the glorious jewel of Terra will be the hardest to crack, what worthy spoils might await along the way.
Using FM3145 to estimate the number of mechs on each side shows that the Wolves and Republic are either evenly matched or that the Wolves enjoy a large (but not overwhelming) advantage.
The Republic has the following number of mech battalions:
Hastati Sentinels: 7 brigades x 3 mech battalions = 21 mech battalions
Principes Guards: 6 bridades x 2 mech battalions = 12 mech battalions
Triarii Protectors: 5 brigades x 1 mech battalion = 5 mech battalions
Stone's Brigade: 6 brigades x 3 mech battalions = 18 mech battalions
Total Republic = 56 mech battalions
And depending on how many mechs per battalion, the Republic fields ~2000-2500 mechs.
36 mechs per battalion = 2016 mechs total
40 mechs per battalion = 2240 mechs total
40 mechs per battalion plus regimental command companies = 2528 mechs total
The Wolves have 75 clusters, and depending on the average number of mechs per cluster, field 2200-3800 mechs.
75 clusters x 30 mechs per cluster = 2250 mechs total
75 clusters x 45 mechs per cluster = 3375 mechs total
75 clusters x 50 mechs per cluster = 3750 mechs total
So at the lower end of each side's range, the Republic and Wolves are evenly matched (at least in mechs in 3145). But if the Wolves are back to traditional mech numbers in their clusters, they could outnumber the Republic in mechs by almost 2:1.
This is admittedly a gross analysis that doesn't take into account other forces (aerospace, conventional). But it does show that just one of the large Clans (Wolf, Falcon, or Bear) knocking on the Republic's doorstep could take on the Republic by itself, although it could be a hard-fought war. If multiple Clans join, though, it appears that the Republic will fall quickly.
Frankly, I personally look at the issue of the other clans not as "What other clans can be made to submit, once we take Terra?" but as "What other clans should we allow to join us in pursuit of a Third Star League?" "Who among the sphere clans is even worthy of this honor?" After all, Nicholas Kerensky did not found the clans by sheer force, he built them out of those WILLING to follow his vision.
Most Clans have subfactions that could join a drive on Terra for one reason or another. Most of the Horses are probably fed up with Malvina, and there is an element within the Falcons that has tried to depose her. The Bears' Omega Galaxy arguably has an interest in the Republic and a border to secure when Fortress comes down. And Fox Khanates could be bought. Only the Ravens don't have a useful internal division that comes to mind.
Similarly, the Republic could bring some allies to bear, too, like the Northwind Highlanders, the Fidelis, the Remnant, and maybe some FedRat commands.
What do people think the fighting on Terra itsself will be like.
Herb once wrote in a BattleChat that Terra will be depopulated at some point in the BT timeline. The creation of the ilClan could be the precipitating event, which might indicate that the battle for Terra will be devastating. Or it could just mean that native Terrans don't want to live under the ilClan's boot and leave for elsewhere. Or the depopulating event could be the end of the ilClan.