Seems like a bit of a hassle to implement imo and a thread discussing the need for a new board would probably suffice. Out of curiosity, what new boards would you suggest? I can't think of any that are desperately needed and more boards can sometimes create more problems than they solve and cause more hassle than they're worth.
For me the main benefits of implementing trial boards is:
It allows boards that are able to garner sufficient user support to be experimented with in real time and can help to determine whether it is worth the time to implement it as a main board or not, instead of an admin or mod being presented with the choice of yes/no to any new board proposals they can try it out first and determine if there is sufficient user support.
It provides a central location for these inputs, previously there would be no way of knowing what boards people want except for a user requesting it by himself in meta then having it buried, this creates a central area where one can submit proposals and have them viewed by the community and remain visible for longer periods of time.
It saves the time of people requesting X board in Meta.
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In my opinion, most boards suffice at present but I would like the new forum software to allow for some experimentation and it's best to code it as a function when its being developed.
I have seen a few meta requests for specialized boards now and then but they get lost in the general context of all the topics in meta and this would provide an opportunity to experiment with them, instead of saying X board would never get enough traffic without having a test case.
If the trial board fails then that settles it and the trial board is removed, if proven to be viable it can be implemented as a new board to the forum.
Presently the main boards that would be worth suggesting some trial boards to in my opinion are Distributed Blockchains fundamentally related to the Bitcoin protocol (Bitcoin 2.0) which is separate from Altcoins and Crytocurrencies or clone coins.
And a Science and Technology level to go with the Politics and Society and Economics.
Inside it a general forum for technology related discussion that is not part of mining or bitcoin discussion but may be worth looking into like a general/distributed computing subforum etc.
And a request board where users propose suggestions such as this one for the new forum software.
An example I hear often enough is a certain forum section was getting annoyed with Ponzi's so it might make sense to try and resolve those type of issues by creating an appropriate trial board and seeing what effect it has in that section.
Another common one is a Sports sub board.
The above are just examples though, they would need to be tested to see if they were worth keeping but that is what a trial boards primary function is to experiment and adapt to the community's needs.
That said it never hurts to have a few spare slots open that can be filled but only if there are enough users to fill up the board.
But you do have a fair point H@C janitors and mods don't grow on trees, and are easily the forums most valued and in-demand resource.