I have seen similar rooms in various people's houses with various combinations of children playing together over the years (DS now 13 so over that stage just about). He had a group of about 5-8 friends who regularly played at each others houses in various combinations and they would sometimes play more wildly than others
Experience taught me:
1 always set boundaries really clearly before children 'go upstairs to play' eg
I didn't mind toy mess but my room was out of bounds and children had to help tidy way at the end (which meant I had to end the play date 10- 15 mins early for them to help do that), after that they had to do quiet time, have a snack if it was a bit early to go home
Another friend didn't mind them going in her room and always just brushed off any mess at the end of the play date, saying she would sort it
Another was clear that any toys played with had to be put back before another came out. She was really clear and enforced this the first couple times (asking one parent to collect a child that wouldn't do as they were asked, though not demonising them as they were welcome back the next time). The children then just knew that they couldn't do any running around wild making a mess at that house as they would be sent home otherwise.
What is important is that any visiting parents support the host rules.
2 Help the host child to put away any really important/precious toys that they don't really want to share before the playdate.
3 - Regularly check on them to see what is happening. If you are unhappy with the mess, make them tidy up there and then if you had said no toys to be left around. Or remind them they will need to tidy up at the end and to treat things carefully not break anything . Remind them which rooms are out of bounds etc. If they refuse to listen then maybe set some consequences.
4 - Get them to come down for a drink/a snack to reset them every 45 mins to an hour
The weird thing is that this definitely did not always happen, sometimes the same groups of friends would play more quietly and sometimes they seemed more rambunctious and difficult to reign in. DH and I used to wonder how we could tell what sort of playdate it would be as it seemed to be random and not always related to the combination of children. We sometimes joked it was probably the stage of the moon that caused it 
Actually some of my fondest memories are of groups of children running around my house playing hide and seek/other games while using a lot of DS's toys as props, resulting in a LOT of mess. Similar scenarios in friends' houses told me I was not the only one who didn't mind the mess too much as long as things didn't get broken etc.
Some friends did mind the mess though, and if we went there I always warned DS in advance and supported the host parent apply their rules. You do need to be clear what your boundaries are though, otherwise your visitors won't know