[Taylor]

I'd say it depends on the resources available and the game strategy of the team.
Resources:
Does your team have access to a fabrication shop with a quick (1-2 day) turnaround time?
Can your team shop make mechanical adjustments on the fly?
Does your team have two (or more) committed and knowledgeable programmers?
Strategy:
Does your driving strategy for this specific game require you to make evasive maneuvers at full power?
Will the weight of a swerve drive added to the type of manipulator/harvester you wish to use put you over the game's weight limit?
Would your team be willing to sacrifice some drive practice time during build season?
Has your team built a swerve system in the offseason?

If the answer to all of these is "yes" then I'd say give it a shot.

I don't think anybody would say starting a swerve from scratch in the build season is impossible, but it is very ill-advised. I would make the unqualified statement that teams should be very hesitant to create any drive train in the build season that they have not successfully made before.

Edit: Al (the poster before me) is a pillar on WildStang - the creators of arguably the best swerve system in FRC. If he says be careful, I'd heed his words.