The concept suggested imo would add to the time to craft rather then decrease it or speed it up in any way. In order to adjust crafting methods need to be developed that would improve the speed at which one can craft a large amount while crafting.

A few ideas come to mind of how this can happen.

For every synth there could be a "spiritbond" like concept where once you reach 100% your ability to synth said item is improved by 50% but you only earn the % on a succesful synth. But of course it wouldn't be as simple as every synth recipe having the same % like the 1-10 ones might take 50 synths to "master" 11-20 150, 31-40 300, 41-50 600 and then rarer more complex synths could take anywhere from 1000+ synths to master them.

By mastering a synth you obtain the following benefits which would always be the same for every synth.
-The Complete rate would only need to be 50% to finish, while you could still continue to 100% to obtain a higher chance for HQ upon reaching above 50% you are given the option to complete the synth.
-The success rate of all your actions are improved by 25% and the chance for ethereal spark is reduced by 25%
-The chance to HQ is improved by 15%
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Another concept for long haul synthing could be consecutive success. This only works when you are making the same synth over and over without changing like logs into lumber. When active at the start of every synth 10MP is consumed for your "Focus". Upon succeeding in a synth you are given a counter of you Focus.

The Focus itself would be static for any item being synthed as long as you don't break the chain. When you complete your first synth you obtain a .5% chance of succeeding. So if you have 200 synths and 2k MP you could in concept improve your odds of Success by 100%. Along with this .5% for every 10 successful synths your completion objective decreases by 5% with a cap of 25% so you could effectively complete a simple synth at 25% if you mastered said synth and have done 50 of the synths in a row. This concept is moreso for mass producing items without it getting to repetitive but giving an advantage for mass producing.

Now with the MP in mind once you run out of MP you can no longer gain Focus for the synth which means the focus you built up breaks and you have to recover MP to start again. With using MP it prevents a person from capping their Focus and then just going crazy on 30 stacks of the same synth lol. With this there is a necessary pause in the creation of an item.

While there are other ideas in mind I feel that these two above would work well in actually decreasing synthing time but without having to dumb it out or change the concept completely.

With the first concept it encourages people to synth to master a recipe so that they can do it more efficiently. As for the other concept with the ability of Focus one can learn to synth faster way before they Master it but it's not a concept that can always be used successfully while skilling up since failing one synth breaks the Focus you built up. While you could attempt to Focus on a synth 5-10 levels higher then you, one fail and your Focus breaks.

But ya, if there's one thing i'd like to hear from Yoshida next Thursday, I'd be interested in hearing more about where they plan on taking crafting and gathering. I hope we can get some of those answers and he's able to flesh them out more as a unique experience rather then a side activity.