I just posted this seconds ago in a similar thread:
Specialty needs fluctuate, but med-surg has no where to go but down and it has been in a decline for the last dozen years. Increasing acuity and shorter hospital stays are killing the numbers needed. Hospitals tend to steer new nurses there as well, cheaper than hiring travelers or even experienced med-surg nurses.
The specialties that stay in demand (but still fluctuate) are ICU (and NICU), OR, OB, and cath lab. ER too. All of those have super specialties that increase marketability and all of these also pay more than med-surg. Supply and demand, right? Tele is somewhere middling. For the most part, even for med-surg, hospitals want tele nurses.