GDevelop now supports tilemap painting with collisions. Read the release notes here: Release 5.4.207 · 4ian/GDevelop · GitHub
We are able to use actors, but building platformer levels from it makes very little sense. That’s why I’d like to request tileset support. If you want to see what I exactly have in mind, please download Stencyl and use it’s scene designer. It support both tiles (which are in tilesets and are placed in grid) and actors which can be placed freely.
A grid exists Game Develop. Just click on “Grid” in “Scene” ribbon. You can configure it to attract object.
Take a look to the ‘BasicPathfinding’ example who use the grid.
Grid is fine for placing actors that has to be at certain position (player start, moving platforms) so it’ll be aligned with other things, but main advantage of building levels from tiles (+actors if needed) is that you can actually draw tiles like in Paint, you don’t have to click to place every tile which may increase level making time especially with big level where mainly there is used grass tile.
More and more platform games are nowadays getting rid of these tiles ( See Rayman Origins for example ) 
But I know it would nevertheless be interesting to have a “tile painting mode” where objects can be “painted” as tiles and/or a “Tiled background” object to repeat an image ( like grass ) over a large surface.