Mark,
Great questions. Thanks for posting.
1. Yes, you can expect that over time the ESW 500 Series will replace the Catalyst Express Series.
2. There are no plans for the ESW 500 series to replace the SRW/SFE switches. These product families are somewhat overlapping, but are targeted towards different types of small business customers and VAR partners.
3. You are incorrect in assuming the ESW is IOS based. It is not.
The attached PDF provides a high-level comparison of the Cisco switches that sell into SMB.
Thanks,
Georganne