You can do this already! Just use a space and an underscore ( _) at the end of a line you want to force a line break on:

Normal “enter” at the end of a line
Only 1 underscore at end of line  _
Two underscores on two lines _
 _
Three underscores _
 _
 _
That's about it really!

Which renders:

Normal “enter” at the end of a line
Only 1 underscore at end of line
Two underscores on two lines

Three underscores


That's about it really!

Exactly as James said, or you can do this:

message 1
[[div style="height:100px"]]
[[/div]]
message 2

message 1