I'm with others here, I think this is a very bad plan and would be very against it being implemented. (I do thank you for making a poll and soliciting feedback here though! That's a great step to staying in tune with your community and player base).
Others have done well to explain why I think a decay isn't good, but to reiterate/highlight their points:
--I don't think you can fairly implement a decay between real time and turn based games, because turn based games have way more leeway with how long turns can be, players will be incentivized to sometimes change up their play speed in order to ensure they have a game completing every X days to avoid rating decay, while real time players have no such manipulation beyond just playing again, so rating decay affects the two groups in pretty disparate ways, further causing issues with comparing ratings of the two groups for arena standings.
--I don't think decay is even fair. While it may be annoying for someone to get a very high rating early in the season and just park on it, why is that player penalized over one who does the exact same thing but just late in the season? It makes no actual sense from a competitive perspective.
--Finally, while I'm not sure I'm in favor of it either, the proposal to use peak arena rating rather than current is also another avenue to solving this issue, but that proposal has far fewer problems in both specifics of implementation and in how players could try to "abuse" the system to avoid it. Rating decay is almost certainly too tricky to set up everything such that you're not just creating a slew more issues in how players try to get around it.
