Err no I don't think what he's proposing her is very reasonable at all and am surprised at some of the advice from other posters.
Contact for a non-resident parent would normally start at one night in the week plus every other weekend. It would be reasonable for you to state that that is what you would like.
Shared care, which is more or less what he is proposing, is great if both parents can truly facilitate that, and the changes can be made in such a way that the child's best interests still come first - e.g. if both parents live locally to one another so shared care doesn't involve massive car journeys every couple of days, or eg one parent doesn't work long hours so that in effect, it's not shared care at all but the child being moved from a home to a childcare setting in order to please one parent's need to feel that they 'have' them a certain number of days.
This last applies to your ex. He can't do the care he's proposing. What he wants to do is take your child away from you and his home for those days, but he won't actually be spending the time with him (whereas you can, being SAHM). That isn't in your child's best interests at all.
As you are SAHM and your child is used to being with you during the days plus your ex is working anyway, I think it's very much in your child's interests for that to stay exactly as it is. It makes no sense to use a nursery and it's an uneccessary change for your child.
As you say nursery, I assume too that your DC is pretty young. Again, shared care of this kind, when it's actually going to involve the child being required to spend more time away from BOTH parents than they need to, isn't generally seen as beneficial.
He isn't thinking in your DC best interests, and that's even before you bring in MIL's likely emotional abuse of your DC (yes, her slagging you off to your child is abusive and will cause much stress - I guess you'll find out about that one as it sounds as if your DC will see more of her without you there either way - in which case don't hesitate to let your ex know if your DC starts showing signs of reluctance to be with her).
To go back to the contact issue - speak to a family law solicitor, and have a google too. It's great that he wants more time with your DC than one night/every other weekend, but what he's proposing is more likely than anything to result in a more stressed, more unhappy DC who might quickly start to associate 'Daddy time' with not actually seeing Daddy at all but being with Granny, at nursery, tired and travelling and pretty unsettled.
If you're still on good enough terms you could talk to him about this and say, I don't want this kind of arrangement and I don't think it's going to work for DC but I do want you to have as much contact as possible - can we think of something better? Contact is supposed to mean CONTACT. Can he take one day off in the week every fortnight and work a weekend day instead, for example, so that DC could have every other weekend, one night in the week one week and the next week have two nights with a Daddy day in the middle? That way, no week would pass without him spending at least two nights on the trot with DC plus a full day or two in the middle?
Reasonable or not, see a lawyer anyway and I wouldn't budge on this one. His plan sounds as if it's tailored to what he thinks are his rights rather than what would be best for your DC at this time of change. I think you would find with such a young DC that you would be listened to in court, especially if you have suggestions to maximise their time together and are clear that what you object to is your child being taken out of your care but NOT being in their father's care for the majority of the 'contact' time.