I wouldn't call any of hEX "successor" to RB5009. RB5009 is successor of RB4011 which in turn is successor of RB3011 and/or RB2011. But there was always a line of hEX devices: hEX refresh is successor of hEX (RB750Gr3) which in turn is successor of older RB750 devices (there were a few). There are a few functional differences between both lines (one is that RB5009 & predecessors have 8+ ports while hEX refresh and predecessors have 5 ports and optionally SFP cage).
It's only natural to see faster components in newer devices (CPU, ports, USB, etc.) but that doesn't define "the ancestral line". So even if hEX pro is much faster than anything in home segment right now (and RB5009 seems to be the top of this segment) it doesn't mean it's replacing RB5009.
Hence I'd say that hEX pro will be part of hEX line (possibly replacing hEX refresh which actually has miserable performance compared to contemporary devices ... specially so as previous hEX (RB750Gr3) was a pretty decent device for its generation.