While it is definitely possible, I wouldn’t recommend Defold for this, even taking into consideration how much I love it.
Defold’s focus area is just not on 3D and even though there is a tremendous work being done and planned for 3D I think making 3D MMORPG in Defold will make you hate (or love, idk 
) the engine quickly.
If you are aiming for something really, really simple and if you have defined the game really well (not only “I want a game like X”, but very thoroughly analysed what you want to achieve) then I might encourage you to at least try, but otherwise no.
Generally MMORPGs are hard, and it’s not only a gamedev popular meme-ish statement, but it’s true, especially when you are starting gamedev, I am confident enough I wouldn’t recommend you making MMO even with any other engine as some of the firsts or first games 
You know, every component is possible, making RPG in Defold, making online game in Defold, making 3D game in Defold. It is possible, yeah, but it’s a lot of work and as above, I wouldn’t recommend it in described circumstances.
As a Proof of Concept, check out The Unnamed Game by @TomRuth - ambitious online game made with Defold:
There is a ton of work behind it.
After all those disclaimers, answering your question:
Yes, it is possible. Yes, it might take few years. There is a Vulkan extension for Defold already: GitHub - defold/extension-vulkan: Enables support for Vulkan graphics
If you checked it already and you mean for the better support for Vulkan - what do you mean by this?