why doesn't Netsight Extreme Management Center support sflow ?

[JohanHendrikx]

XOS switches support sFlow, Extreme Management Center only netFlow.

I hoped that EMC was able to manage sFlow configuration.

Is there a roadmap for this?

[Jesse_Ohlsson]

Then, why do some Summit switches not do NetFlow?

[Frank_Thomas]

If configuration is the primary concern, it's easy enough to use the scripting engine to push. If Collection is primary concern, you can look into Extreme's DSSC as a potential option.
http://www.extremenetworks.com/resources/security-analytics-g2-siem/

[Zdeněk_Pala]

You can also consider Scrutinizer as our technology partner, to see sflow stats.

[Ronald_Dvorak]

To add to that...
ExtremeAnalytics is a add-on to EMC and is not included in the product/price - so you need to buy a extra license for streams to collect/monitor.

You don't need to have netflow collector running on every switch.
It depend on the network design,
Could be that it's OK to have it only running on the Core and or DC switch to get all data that you need.