In the underlay it's all still very much basic, old fashioned networking using existing protocols: BGP in the DC at FB and MSFT, and BGP, ISIS, MPLS in the WANs. (AMZN likes to pretend they're special so I won't comment on them.)
Google is a bit different, in part I think this is due to their culture and early scale they were forced to drive a lot of developments wrt merchant silicon use, and this naturally led them to their own network OS solutions, with a simplified semi-centralized IGP solution for their DCs, and centralized-TE solution for their inter-DC WAN. It's not entirely clear to me if they would still feel the need to do this if they were starting again.
No. It's just going to look different, with the most successful vendors selling flexible, nearly white-box hardware with good long-term maintenance terms.
> if you think a lot of infrastructure will be moving over to the cloud (because of cost pressures) over the next few years
There's certainly going to be a TON of infrastructure moving to 'the cloud' in the next 5-10 years, but cost isn't necessarily the strongest driving factor pushing cloud adoption. Big, established Enterprise-with-a-capital-E type businesses are often quite capable of continuing to run infrastructure in-house with better bang-for-buck in terms of raw capacity than what is presently capable with public/hosted private cloud solutions.
A while? More like forever. Short of corporations abandoning the notion of shared physical workspaces (which isn't likely to happen in the foreseeable future), corporate MDF, IDF, and edge gear will always be around in some form or another.