A mint4win LMDE - that is, a loop mounted image file would look something like the screenshots at this link would it not?
People have asked why no mint4win for LMDE. The wubi developers give the clue when they say that the Ubuntu kernel is suited to this type of install. Unzip the initramfs of the Ubuntu and Debian kernel and compare. Try booting an image file with the Debian initramfs. It can't find the /sbin/init file on the main file system - my reading is that it does not have the support for loop mounting. Well I don't have the knowledge to create a kernel - so why not make a funtoy hybrid? A LMDE filesystem on an image
file using the Ubuntu kernel to get a boot. Now up and running on a 10gb image on a USB HDD.
Wubi or win4mint seems to polarise opinion quite strongly, perhaps because of recent history problems with grub updates & also the different booting method introduced with Vista/Seven compared to XP. But I'm on the love & adore side of the fence. Fragile? I've hard closed my ubuntu wubi & win4mint wubis dozens of times - never had a problem.
And backup? A single file, that's it. Going through a full new install - simply migrate the disk image to a USB HD & you have a ready to go full spec mobile system.
So, No there won't be a win4mint LMDE because the Debian kernel can't support it but there are alternatives.