Do you realize the amount of work that this would require? Even approximately?
using the latest witcher engine/tools
There's no such thing officially and the community tools are serviceable and that's the best stretch - making a single coherent quest with them is already a hefty task, redoing single games worth series of complex quests which would also affect other quests is far beyond the scope. Redoing both games is even less likely.
That's already counting out the requirement to make entire new areas and assets.
Even with competent tools this would take a team of competent enthusiasts couple of years to complete, W3 modding community probably no longer even has enough people to assemble such team (assuming all of them would be interested) not to mention that tools are also sub par for such task.
To clarify the famed "Witcher 1 prologue remaster" took erx (with help of other people) around 5-6 months if i remember correctly - that's with literally reusing existing area of Kaer Morhen and most W3 NPCs/models with only Frightener being backported from W1 (and still being just a reskin of existing monster)
That's a single 30-40 minute quest where most of the stuff was already existing in Witcher 3 and only matter was to string it together to be functional as a quest.
So yeah, in TL;DR you got a nice dream there buddy but it's not gonna happen.