Sharding a MongoDB instance by a spatial key and a date
my question is to know if this is feasible


A shard key index cannot be multi key, text, or geospatial, so part of your theoretical approach is definitely infeasible. You also mention considering hashed sharding on a datetime field, which could provide better data distribution for otherwise monotonically increasing values like a timestamp. However, a tradeoff is that hashed sharding does not support range queries since adjacent source values will now have distributed shard key values.


  also if mongodb will be clever enough not to split according to the spatial key unless I manually ask for it?


Since a shard key cannot be an array or geospatial value this specific question doesn't really apply.

The default behaviour of MongoDB sharding is to allow shard key range splits (aka "chunk splits") to happen automatically so that the sharded cluster balancer will redistribute data between shards based on chunk imbalances. It is possible to adjust the default behaviour (for example, disabling autosplits for a cluster or balancing for a collection), but you should only do this with careful consideration. Micromanaging a sharded cluster can be counter-productive.