If I remember correctly, DISH was threatened with Lawsuits over the sling technology as broadcasters feared people would be sharing their accounts and non subscribers would be accessing their content. So to avoid those issues DISH agreed to limit it to one stream and built their Sling Encoders to handle only one stream.
BTW the Roku does not support DISH Anywhere. However you can cast from your phone's app to your Roku as a work around.
IIRC, The Sling technology as developed and later purchased by Echostar/Dish was always limited to ONE stream/one user per stream because that is natively LEGAL. The ONE stream per user
PER DEVICE at any one time is what made Sling "Bullet Proof" from lawsuits from content providers and owners because that limitation kept the device within Fair Use. Any additional streams or additional users PER DEVICE would be OUTSIDE of the Fair Use of "personal" and "private." So, one could always buy MORE Slingboxes for as many people to use ONE at a time even in the same household. This is also why households with 2 Hopper boxes with Sling built-in may have more than one Sling stream from the same domicile/account because the issue is ONE user PER DEVICE at any one time, just as it always has been with Slingbox before Echostar/Dish bought Sling Media.
More than one stream or multiple streams and multiple users at the same time using the
same single device would require accessing "Digital Rights" or payment to the content providers, meaning that the content providers can require payment for any and all additional beyond the ONE PER DEVICE because anything more than ONE PER DEVICE takes it OUT of Fair Use, and a violation of copyrights.
Now, if Dish had plans to provide "multiple" PER DEVICE without paying the copyright holders, then lawsuits would be a coming--unless Dish pays content providers for additional PER DEVICE. The other MVPD's do offer multiple users at the same time, but they have obviously PAID the content providers to give them--the other MVPD's like cable cos.--a competitive edge, or something subscribers want. It is probably expensive to obtain such rights for "multiple" and Ergan does not like anything expensive if he does not see it as necessary. If Dish wants to provide "multiple" experience PER DEVICE through its Sling technology (presuming it can be done with the Sling tech), then all Dish has to do is PAY the content providers to do so, and they WILL gladly take the money because that is all they are about: the money and more ways to make it.
I would also add that Slingbox offeres a feature that allows Slingbox owners to allow anyone we choose to be "Guests" of the owner of the Slingbox, a feature that allows another person to be provided conditional access (fully revocable by the owner of the Slingbox) to another person's Slingbox to stream content with the creation of a seperate account so that the owners username and password are preserved solely for that owner. Nonetheless,
this practice amounts to account sharing, and this is LEGAL because the issue is not necessarily WHO is using the Slingbox to stream becasue Slingbox does not require recurring payment for use per account, so we OWN the Slingbox, and we are not required to have a license to use the Slingbox granting us EXCLUSIVE use of the Slingbox, but rather it is only the issue of ONE person streaming on any SINGLE Slingbox (ONE PER DEVICE), at any one time, which is legal and within Fair Use, allowing Aunt Betty 1000 miles away to view anything connected to MY Slingbox in another state anytime she wants to access my Slingbox for her own PRIVATE and PERSONAL use, but only ONE of us can access the Slingbox at any ONE time.
And, of course, any copyright material has entered my home LEGALLY such as making any required payment to access that content, so, yes, anyone else may remotely access my Slingbox at my invitation to watch my legally obtained copyright content for that remote viewer's PERSONAL and PRIVATE use.
And despite the Terms of Use of the streaming services forbidding "archiving" (like a DVR) any of the streams, we, in fact do have the right to "archive" anything we stream (so long as we obtain the material legally such as a paid subscription if required, and it is for our PERSONAL and PRIVATE use) on our own local storage for later viewing. The catch is how to achieve this ability. Well, the internet offers LEGAL options and even legal services to make that possible, especially if the "recordings" takes place AFTER decryption, such as the rendering phase. Saving the stream at that point protects the streaming service (it has fulfilled its obligation as far in the process that it can control), and is also perfectly legal for the individual consumer to "record" and save that streaming content for personal and private use.