Suggestion 1: SKETCHER
We all LOVE the delete Segment tool that has been around a long time. Can you have another tool that does the inverse???
When I drag a line across 2 lines it could automatically extend them until they meet at a corner. If the lines are parrallel I guess it would automatically "forget the first line that you crossed, and wait for a 3rd line that can form a corner with the second. I hope I am not making this more confusing than it is..
Could call it "Corner Segment or Extend Segment..... with a green squiggly line on the icon and 2 perpindicular lines that don't current meet at a corner" This could be a flyout for the "CORNER" tool as another option
Suggestion 2: SKETCHER
When I am in sketcher and have sketched a box, I want to be able to pick on a corner of the box to place a radius that is trimmed and automatically tangent. Similar to picking an edge in modeling mode to place a radius. This may be tricky because the point would have to know that it is a corrner and not just the end of a line segment. But I suppose the command would just not work if you picked a point at the end of a line. It would be a great feature though and save time.
You have enhancement ideas section where you can post them.
While not precisely what you've asked for, both tools already exist in Creo and have for some time.
The "Corner' tool, directly under the "Delete Segment" tool, will extend two engagements to an intersection. Select "Corner", select segment 1, select segment 2.
The "Fillet" tool works similarly to trim two segments to a fillet. There are options in the drop down for Circular and elliptical fillets and for trimmed or not. Trimmed is a little misleading as both trim the existing segments. The "Trim" options actually eliminate the trimmed portion, the others leave it but make it construction geometry so you still have the intersection.
On a related note, has PTC made mention anywhere of a timeline for Creo 4? It's not on the product calendar yet.