I think you are looking at it the wrong way. What is the reason not to have it? I personally have ipv6 only hosts at home as I have only 5 static ips but a /56 from my internet provider and a /59 from he.net. I have tons of v6. If I’m remote and want to connect to my home server I require ipv6!
I currently do this with a laptop due to Roku limitatIons.
Any streaming platform that doesn't support IPv6 in 2022 is doing the entire Internet a disservice. Google, Netflix, and the other major streaming services support it, and their Roku apps would use it if they could. I don't care if Roku uses IPv6 for its system management, but they absolutely should have the stack available for modern apps to use.
Supporting legacy IPv4 is expensive and enforces inequality which favors those older providers which were able to get large IPv4 allocations years ago.
Any new ISP starting up (or significantly expanding) today (especially in developing countries) will not be able to get enough IPv4 to provide to customers, at least not at an affordable price. They will use CGNAT - that is sharing a single IPv4 address between hundreds or even thousands of customers. The only providers that have enough legacy IPv4, are those in saturated markets where their customer base is static or declining.
The side effect of this is that the connection is slower due to the extra overhead of CGNAT, and because all the traffic for many users originates from a single address it is likely to get blacklisted from services (eg if one user does something malicious or gets infected with malware). CGNAT also creates other problems for the users.
This makes using the internet over legacy IPv4 a quite painful experience in developing countries. People in developed countries where ISPs typically provide each customer their own IPv4 address tend not to care. This ensure that developing countries are held back.
IPv6 is plentiful, putting everyone on a level playing field. Everyone can have their own block of IPv6 and be a part of the modern internet, not an outsider peering in through a slow and congested CGNAT gateway.
Use some technology that allows multiple residential clients use the same IPv4 address. As more clients have to use the same IPv4 address, there are several down sides, the first that a Roku user may run into is throughput as a box would have to do translations between the port and address on the Internet side to a new port and address on the client side. The second issue, once too many clients are being mapped to the same public IPv4 address is a limit on number of simultaneous sessions, which may impact some of the channels on the Roku if used at a home with a bunch of simultaneous game players or streamers or PC users, if the session limit for the home is reached it may cause a channel on the Roku to malfunction.
ISPs that just cannot get enough IPv4 addresses, even while using a technology that allows sharing of public IPv4 addresses among clients, may end up with clients that have only IPv6 addresses.
Having the streaming box be dual-stacked (being able to use IPv4 or IPv6) would avoid the performance hit and other issues that public IPv4 sharing technologies may cause by allowing the streaming box to use IPv6 where available.
No, it won't take more memory and resources. The Linux kernel versions in use by Roku have supported IPv6 for years. Shortsighted consumer electronics vendors have already had problems with IPv6 network providers here in North America, c.f. Tablo remote access & T-Mobile wireless. Wireless ISP's, Satellite operators, & other new entrants are and will continue to use IPv6 transition technologies and native IPv6. Come on CE vendors, World IPv6 Launch Day was 2012. AT&T High Speed (VDSL) & now fiber have been dual-stack for many years. All the major cloud providers and content delivery networks now have (admittedly varying) IPv6 capability as well.
As an aside, it appears from browsing Roku's source tarballs, that different hardware versions use different kernel versions even for the same Roku OS release. That looks like a ridiculously complex testing challenge to me and likely explains some of the odd bugs that pop up after every new release affecting mainly one hardware version and not others.