HDMI 2.1 is not required for 4K/60. HDMI 2.0 is, and any 4K TV will have that level. In fact, I just looked at the specs for the latest Roku Ultra (model 4800), and it says it comes with HDMI 2.0b, not 2.1. So I'm not certain what you read where.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.