Playing Shaka on an all land map is as balanced as Ragnar on an Archipelago.
Surely not - the AIs seriously suffer on watery maps, and are a lot better at this kind of all-land thing. Maybe you'd have a point about Shaka being great, maybe too great, at this kind of map but with AggAI turned on I think early rushing will be a lot more difficult. Also, while you are embroiled with one war all the other AIs will be amassing troops and can attack any player at any moment. This gives the computer players a significant advantage which is precisely the opposite of the Ragnar game.
I vote Inland Sea.
At first I thought that Lakes would be OK, until someone mentioned the tundra strip. Yes, that's bad and will force you to go for conquest, unless you want to settle those frigid lands. (I almost did that in a Highlands Map game before I retired). Maybe you can build those cities then gift them to your vassal, because vassals do not stop a conquest victory IIRC.
Had a look and Inland Sea is quite an artificial looking map type; you get a bit of tundra at the top and bottom but then the big black border appears. I didn't play on for very long, does anyone know if you can actually zoom out to get the full planet-in-space view using this kind of map?
About the map, I looked at some Lakes maps, and my impression was that even with high sea level, it's A LOT of land, and the lakes aren't big or numerous enough to create anything resembling choke points. That should help AIs that are good at rexing, but also be a big help to Shaka who not only can rex very well thanks to the Ikhandas, but who can also just keep rolling over one opponent after the other. I think I'd really prefer two to four continents with at least one opponent on the same starting land mass so there can be an early rush but it won't become too straightforward.
Yes it's a lot of land, but high seas can sometimes make a difference. I agree that it's not quite as full of choke points as I would have liked, though.
THe thing about Shaka is that he is just great at total war; great UU to spam, great fast-building UB to save money, and pretty good traits. We all know what the strategy for this game is going to be regardless of the chosen map etc: Impi spam. All being well Sis should be able to crush one or two neighbours and then assess his situation; this is where the choice of map comes in: if you're playing a continent-like map, you may have already taken over your landmass and can sit pretty, building up ready for the inevitable invasion of the other landmasses - should be a cakewalk. If you're playing an all-land map however, there is no point where you can feel safe from AI invasion (and no border which is safe!), and the AI WILL be spamming units. I really believe that a continents map type would be a lot easier for Shaka than Lakes, Inland Sea or any other all-land map would be.