Sundaland Map - Work In Progress

I've been working on a map for the Sundaland region based on various maps I've found online. There seems to be quite a lot of information about where rivers where probably located and the type of vegetation that was likely present. I have no idea how accurate these are but I'm going to include them anyway.

Some of the maps show a landlocked sea to the east of the Thai peninsula and I'm wondering if I should include it in my map?

Here's one of my source maps without the inland sea.

And here's one with the inland sea. Which one do you think would be more interesting?

Here's Indonesia overlaid on top of maps of Europe and North America to give people an idea of the scale of the area. The inland sea would be the equivalent of one of the great lakes as far as I can tell.