The reason we don't have trading is that it is too open to abuse.
And yet,
every game I know of allows for free trading between players, with only one or two that don't, of which The West is one of them. It's practically a requirement these days that games allow trading. Can it be abused? Sure, but if all the popular online games can manage it, then I'm sure The West can too.
As for the suggestion itself, I think it's a great one. The process for hiring someone has to, ideally, be fast and hassle-free or nobody would bother with it. It would have to be cost-effective and competitive with normal builders that are the town members, while maintaining a balance that town affiliated workers are not put out of a job. The ideal situation is that "hired hands" are more effective in some cases, while in some cases they are not. One situation would be if the workers leave on vacation for a week, the town hires paid workers, while normally the town's worker is the one building. Or if the town wants to rush through a building, and hires workers to make it go faster. If the hired workers were always more cost-effective, though, then ovbiously town workers would not be needed anymore, unbalancing the game.
Conclusion: This would require large changes to the game, however it goes hand in hand with the "town guard" ideas (which look like they have enough support based on polling results), that this could be easily implemented under the same system, and is a good idea to allow builders a way to make use of their skills, as guarding will be for soldiers.