Yep I know plenty of breeders who will plan to have more than one litter due at around the same time. Say you have 4 queens it makes sense to plan to have 2 lots of 2 litters rather than 4 separate litters after another, it makes it easier in terms of time off work, and allows more kitten-free time in the year for life that has some semblance of normality as well as concentrating more on showing during those periods
It's also useful in that if one queen has difficulties nursing, not enough milk or mastitis or some other complication, there is another lactating queen with kittens of around the same age who may be able to help out and ease the burden of the 2 hourly hand feedings.
The breeders I talk to love having kittens around, they wouldn't do it otherwise, but it is an exhausting business and most agree that it's better to plan to have times of the year with no kittens so that they can recover, it would be more difficult to do that if you only had one queen with a litter at any time
3 or 4 queens being mated at times to deliver so that there was only ever one litter at a time would mean you'd have kittens constantly without any let up!