A way around the variable length (to a certain extent) is to make adjustable pieces, kind of like this but mirrored so that there were the thicker parts on both ends. Obviously this would be a bit tricky to construct, but I think it could give you the function you want.
First off, +rep for that pun-ishing picture of a telescoping arm bracket. I did think of that but quickly nixed the idea when I got rolling with thoughts on execution.
Lengths would vary, but there is enough consistency in tile size that it would work out. If that doesn't make sense I can take quick demonstration pics when I get home later.
Honestly man I appreciate the effort but the variable walkway lengths just isn't worth pursuing from what I experienced trying to make them line up using the paper cutouts (there were a ton of varied sizes, even started taping some together to experiment more). I was looking at having to make 20+ connection bases and so many varied pieces of walkway the project would still be under way by the time plastic Sisters of Battle get released
It was really way too much work, and not even the fun kind where I hand push 300+ brad nails into foam to represent rivets. It already takes a fair amount of time just setting the tiles down and making it all make sense right off I really don't want to have to think about how I'm setting down terrain elements to make walkways work between them, or sit there going "I know I made a damned 6 inch walkway, it has to be in here" while desperately trying to make things meet on a table where it's up to my walkway collection to make the connection.
There will still be plenty of walkways, but they will be more bridge-like instead of the 'main' level of play. I constantly get different ideas "but this will connect if I do it this way" but it always ends up being "OK, that will connect if I set the table up this way but what about the other dozen ways it can go". If you have time to kill and want to draw something up by I'll gladly check it out but as you can see I'm pretty well moved on from the idea. Only thing stopping me from executing more terrain building is my Blood Angels, who are getting entirely revamped for 8th edition.