Not sure I understand your question. The Roams will need to be on WiFi in order to be set up in stereo, they don’t work as a stereo pair on Bluetooth. Using Bluetooth, you can only send a signal to one at a time. 

Beyond that, you buy a pair. I don’t understand what ‘doubling up on features’ means. 

Hi thx for response. I want to buy two to use in a room off of my s2 Sonos system as a stereo pair. I want one to be Alexa enabled and the other one dumb I guess they’re cheaper? So do I need a roam Sl without Alexa and a roam 2 or just roam with Alexa? Hope that makes sense

Oh, I wasn’t reading your topic title. Any device labeled SL does not have a microphone in it. While part of your Sonos ‘system’ it can be controlled by a voice command from another device, be it a Sonos speaker with a microphone, or a third party device (Amazon Alexa or in some cases Google Home devices)

There is no Sonos 2, so I’m up unsure of how to answer that part. 

All of this is covered in the marketing pages for each device, under tech specifications, at www.sonos.com.

Roam Gen1 is not produced and sold any longer by Sonos. Roam Gen2 is the updated device but imo just has minor changes as for example longer battery usage and a dedicated bt button. 
Roam SL is equivalent to Roam Gen1 but without voice control. 
You can pair any combination of those as a stereo pair. One of them with voice control support is enough to make the stereo setup voice control ready. 

If they’re both on your WiFi, there is no reason not to get a regular Roam 2 and a Roam SL (if there is such a thing?) I’ve not looked at prices, but I’d honestly just get two of the Roam 2s, it would be easier.

You can always call Sonos Support directly to discuss it, too.

Sonos answered my question. You can only stereo pair 2 products that are the same model. So two Roam 2’s is the way forward. Alexa commands will be understood as one command by stereo paired speakers. 

To be clear as  ​@Airgetlam commented the Roam2 (or any generation) will only create a stereo pair when on WiFi. Alexa is only available when on WiFi a well. 

I just can repeat that Roam, RoamSL and Roam 2 seem to be declared as one model. There are many users who confirm that a stereopaar (on wifi) is possible with any combination of two of these three speakers. 

Yes it was confirmed that stereo pair MUST be same model and type ie two roam 2’s and on WiFi only. Hope this helps

If someone from Sonos support told you, that you must have two devices of exact the same type of Roam, I suppose she or he was wrong. So imo no need to buy two Roam2 if you like to safe some money.