They could offload the processing to a device that does. They currently do this for personal requests. Putting 8 gigabytes of RAM in a smart speaker is a bit silly.
8 gb of RAM may be a lot for the average smart speaker, but not for one that costs $300. Then again, we know Apple prices RAM like it’s made from diamonds and unicorn queefs.
What would be interesting to me is if they could somehow hand off devices in close proximity. E.g I have an iPhone 15 so no Apple intelligence but I have a Mac and an IPad Pro M2 so if it could utilise those devices for the query and sync up I wouldn’t mind a wee delay.
New Siri was not announced for existing HomePods. That said, there is an Apple event on Sept 9, so more products that support it may be announced.
Most folks are not expecting Apple intelligence on existing HomePods or AppleTVs. It would be very Apple-like to gate the new software behind a new hardware purchase.