I'm currently working on a game where you craft rockets, and I have to jump through a lot of hoops to make this somehow work in C3.
If the Tilemap plugin would be able to rotate this would make it sooo much easier for me to make this game, but more importantly it would allow me to do so much more fun things in the game too. Right now, after the player drew their rocket with tiles, I need to paste the tilemap into a drawing canvas, then run a marching square algorithm, that 
R0J0hound wrote in JS, over the pixels to detect the edges and create a collision shape via a distorted mesh.
I could avoid all this if the Tilemap plugin was able to rotate, and I would still maintain the ability to change the tilemap unlike with the pasted image of it.
This is also not the first time I ran into this, wishing it was possible. I wanted to make an RTS once where you build your own tanks out of tiles, but I had to drop the idea because of this limitation. I can easily think of many more examples, like a space game where you can upgrade your spaceship by installing new rooms and modules, or a construction game where you construct buildings, but if you don't add enough supports, pieces can break off. Etc. etc.
I bet you have many idea for a games that would be possible, or way easier to do with rotatable tilemaps yourself.
You can also not work around this limitation easily (or at all depending on your requirements).
If I wanted to recreate the tilemap with sprites and combine them via hierarchy I would not be able to assign one physics behavior to all objects, and if I apply physics to all of them it would become a nightmare of unstable physics or they would not interact as if they are one connected object. Joints do not work for this either because there is no weld joint where everything would acts as one.
Creating your own collision shape is also only possible in this very hacky way of using deformed meshes, and we do not have access to the collision polygon points so you can't just try to only take the outer points from the collision polys you already have, you need to use approximation algorithms like marching square to recreate new collision shapes from scratch.
The 9-Patch and Tiled Background plugin already got rotation added and they became so much more useful and versatile because of it. I know that the implementation of angles for the Tilemap plugin is quite a bit more difficult than these two, but the increase in versatility this would bring is immense and would open up so many possibilities for the C3 community. I hope this improvement to the Tilemap plugin is considered by Scirra.
I added a suggestion on the suggestion platform https://construct23.ideas.aha.io/ideas/C23-I-522, but I don't have high hopes for many votes.
The problem is that feature improvement suggestions often die on there simply because it's not a shiny new toy.