To summarize from Discord and kick off the discussion on the forums about Uriel V's invasion and the fallout in Morrowind.
Going by this map:

And this expansion into the unknown east:

We had some big and long discussion about how and where the invasion took place and what the fallout in Morrowind might have been.

The preliminary points were:

• Legions travelled from the west either via boat, either from Skyrim (north of Vvardenfell or by the Inner Sea), Cyrodiil (to Narsis, then either north to Ebonheart and Firewatch via Thirr and Inner Sea or east through Almalexia), and Black Marsh (mostly by ship),
• Uriel V needed to have set up several naval supply/repair bases to supply his invasion fleet, along with a supply fleet and a rear guard to keep the water free of pirates and enemy ships looking to interdict the supply ships,
• Severeal additional Imperial forts would have to be constructed at the coast or on islands east of Tamriel, most of which would have fallen into ruin after the disastrous defeat,
• Turning the geographic divide into a strength, there would have been two forward ports where the fleet gathered and went after Cathnoquey in a two-pronge invasion from friendly ports, afterwards tackling Yneslea from one friendly and one hostile port,
• Following the defeat in Ionith, some more Imperial forts would have been constructed to form the "Eastern Shield" against the expected Akaviri counterinvasion, of which Drakehold and a lot of the eastern navel bases have fallen into ruin when no counterinvasion happened.

Opportunities for TR include:

• Rebasing the Ruinous Keep exterior (which is not that well-placed where it currently is) as an island port south of Necrom while keeping the interionr and quest largely intact,
• Redating Bal Oyra as one of the ports which grew into a little town due its fortunate location,
• Adding an additonal Imperial port to the Mudflats; as Uriel V was very good at externalising internal problem, this could have been paid for with a Deal to never strike Imperial power into the Deshaan proper as long as this port stands; there could either be a totally isolated penal batallion in the port or a Dres clan who keeps the port up in shape just so that the Empire cannot enter the Deshaan,
• Adding lore that extends beyond the Armistice into the intervening years, which is currently still awfully lacking. The triuphant marsh of the conquering legions to the eastern ports through Almalexia (and the less glorious return), the deal with the Dres, the panic and collapse of the aftermath which the Dunmer would have felt and seen.

Additional maps to make the sheer scale of the invasion more clear:
https://cdn.discordapp.com/attachments/401794229476655105/410167541248425985/unknown.png
https://cdn.discordapp.com/attachments/401794229476655105/410168681042280448/unknown.png
https://i.imgur.com/jEBLiat.jpg together with https://cdn.discordapp.com/attachments/401794229476655105/410172057746145290/unknown.png