Its not uncommon for people to ride Cyclocross in the winter and Road/MTB in the summer.
How do you avoid burn out? Do you follow the Base/Build/Speciality twice in the same year or do it once to target your main goal and then fill in the remaining weeks with TR workouts that work for those other events or possibly a Maintenance plan?
It’s a delicate balance and different for everyone. Listen to what your body and mind is telling you and if you think you need a break then you most likely do. The past season I did Traditional Base 1, 2, 3, Build, SSB 1 &2, Build, then Specialty into my “A” race. After my second Build I took a week off the bike followed by a MTB vacation. It was desperately needed and re-energized me for the remainder of the season.
I mentally check in the winter and my focus is on other things.
I’ve burnt out twice during the winter and its not the act of riding that burns me out, its bicycling being all consuming. Ride bike, post on bike related forums, stare at stravas for an hour, socialize with people on the bike, dream of winning my next race. When I’m racing this sport just consumes every inch.
So right now I’m just doing my workouts and playing video games, but I’m more into the games. That’s what consumes me right now.
Come March when Tuesday Night Worlds come up and I podium the fake race and everyone high fives me like I’m Maverick in that scene on Top Gun, then it’ll come back 
I ride whatever bike I want 3-5 hours per day in December, January, February, whatever and don’t ride inside unless the weather sucks and I need to make caloric space for beer and food. CX season is over, I casually race MTB, so I build a shitload of base and eat pastries at this time. Get a big handlebar bag, go for a ride featuring some dirt/gravel , stuff bag with pastries, enjoy life.
I’m still trying to figure that out…
I don’t race much in the summer, just the odd one, but I ride a lot. I find it hard to fit in a proper base-build cycle, and feel like I’m always playing catch-up with the roadies who start training in December/January.
This year, I’m planning to finish cross a bit earlier (not in March), and have some more time to chill before starting training again. Lots of the fatigue from cross for me is mental, it’s the long days out in the cold and wet, and hours of bike cleaning in darkness.
Don’t poke the bear too often.
I consider any zone 5/6 workout, and any race “poking the bear.” You are placing a high sympathetic load on your body and mind, and there are only so many times you can do that – especially if riding your bike is not your job.
2 x 4 week Build Cycles = 14 days of poking the bear
10 races = 10 days of poking the bear
1 more 4 week Build = 7 more days of poking the bear
4 more races = 4 more days of poking the bear
35 days is a whole lot of poking. Throw in group rides during Base that turn into the “poke days” and it gets even more taxing.
Everyone is different, sure, but I’d say a conservative limit would be about 30 days to poke the bear in any given year, if you’re a masters-age rider.
That sounds exactly like me. I have plenty of hobbies but I naturally want to obsess over one at a time. When cycling takes a back seat to another activity, I just wake up early and knock out the workout and that will be the last I think about it until the next session. Sweet spot stuff and threshold work burns me out more than anything. VO2 max gives me the runner’s high endorphin rush so I always look forward to them.
No science or source, just the observation that most 40+ weekend warriors with jobs and families get a little crispy after about 30 days of accumulating 20min or more in zone 5-6. Something like 5 x 4 VO2, or a XC Mtb race, or a 'cross race, kick in a big sympathetic fatigue response, and a little of that junk goes a long way.