I found it quite cumbersome to create pieces of land, bordering on the sealine, and then, they are "only" 5 Km wide at best, with water to the left and right, always suggesting an island rather than a "continent" when approached from the seaside....
There are certainly scenarios for which this is inconvenient (e.g. the starting scene of "Predator" ) .

Not sure whether this can be overcome using an imported custom heightmap, since opposed to these, the terrain generator creates infinite (looking) terrains. It is clear that the EDITABLE part of such a coastline will max out at 5Km width anyway, but that is another story (and most likely enough for the scenario(s) I have in mind).
Any ideas ?

Why not, once the terrain is in the actual editor (not the Terrain Generator, but the editor that comes afterward), use the terrain editing tools to sculpt the terrain to get what you like? You can raise the other side, for example, to make the sea on that side go away, etc. The Terrain Generator is kind of meant to be a beginning point. Then you take the terrain sculpting tools and complete the task, sculpting the terrain to get what you envision.

i was wondering this myself.
Not just seas and oceans could be problematic, it could be any body of water.
For example, what if i need a river that runs beyond the area of editable land. It will look really rubbish if it just 'cuts off' within the 5km square.

You mean something like this
Quickly made from this


the bay area was the playable area by the way.

go here. find a place you like, render, export import into max, BOOM anything you want. super easy.

https://tangrams.github.io/heightmapper/

@ThomasG81 Yeah, pretty much. The not-so-funny thing is, that the river water (which is quite good with its muddyness) usually looks totally different from the sea water it runs into, even if one confines oneself to the 5x5KM area.

Yeah, Necrym59 & Casigus, thank you both. I was aware of this option/solution, of course.
Not that it is bad, infact yours looks pretty good, Necrym59.

Only I'm not sure where the (reasonable) limits for this manoeuver are. Admittedly, the wider/longer the desired coastline is supposed to be, the rarer the use case ( say, a Space Shuttle flying in from 8.000 mls high ), so i don't really mean to press tgc to implement this with the terrain generator. But in theory, the terrain generator should be able to create arbitrarily long shorelines (only not now or for the foreseeable future). It just m i g h t come in handily for a few of us.