I would start to worry that the quality would start to drop heavily if it became yearly even if worked on by two different teams. So far I view DGS as a side project more than anything with a bigger AA6/AAI3 in the pipeline. Also franchise fatigue is real for a general audience.
Hm... Let me check the very original AA release dates in Japan for reference:
AA = 2001
AA2 = 2002
AA3 = 2004
AA4 = 2007
AAI = 2009
AAI2 = 2011
PLvsPW = 2012
AA5 = 2013
The original GBA releases were practically one year apart from each other, at which pointafter the 3 year gap until AA4notable releases in the series came out 2 years apart from each other (excluding PLvsPW).
Unless it's as GSR theorizes and the series becomes successful enough to have yearly releases between two different teams, it might be unrealistic for that to happen. I really have to wonder about series fatigue, though. When we consider so many games that operate so mechanically similar to each other that have yearly releases (though I suppose it's different when they're AAA titles), I feel like new adventures on a yearly basis wouldn't feel out of place. Haven't looked into it. but isn't the Professor Layton series practically yearly?
Wouldn't want anything that'd impact the overall quality, of course, but I would definitely not be opposed to new cases to enjoy every year.
Also, DGS isn't really a side project, according to Shu Takumi. He essentially confirmed that the DGS line of the series, specifically, will be having sequels in interviews a while back, and it seems that it will be on the level of either AAI as a spin-off, or even larger.