Am I completely wrong in thinking that this isn't really e.g. "removing delimeters", but effectively changing the delimeters into invisible markup?.. It seems to me kind of an arbitrary distinction whether the way you represent a string to a compiler is with quotes or markup that renders a green box.
As far as the concatenation thing surely that's solvable by a grammar that interprets a single line list of expressions as an implicit concatenation. It doesn't seem like something that requires a particularly smart compiler - or a new IDE. Maybe I'm overlooking something inherently hard about the problem though.
I think the deeper point is not about the highlighting, but the ability to interact with the code semantically. If your editor was completely aware of the semantic structure of your code, it could provide very powerful refactorings that respected line-associated comments and things like that.
For example, it you would type a string, and wouldn't need to worry about whether it is represented as multi-line string or not or how to properly escape newlines and special characters. Your editor would know that you are typing a string and do the appropriate thing.
That said, many advanced IDEs do have very sophisticated syntax parsers which can do many of these things already. Light Table and Lisps evolve this even further. I would imagine that a language designed with this use case in mind would enable even tighter integration with the development environment though.
As far as the concatenation thing surely that's solvable by a grammar that interprets a single line list of expressions as an implicit concatenation. It doesn't seem like something that requires a particularly smart compiler - or a new IDE. Maybe I'm overlooking something inherently hard about the problem though.