I did check other thread and did confirm Sigma Designs chip specifications--
EM8620L Series
Digital Media Processors
The EM8620L family provides highly-integrated solutions for products requiring standard-definition and high-definition MPEG-4.10 (H.264), SMPTE 421M (VC-1), WMV9, MPEG-4.2 and MPEG-2 decoding.
Incorporating flexible, advanced audio/video processing, the EM8620L family enables cost-effective solutions for consumer products such as network players, IPTV set-top boxes, networked DVD players, portable media players and HDTVs.
So technically its not limitation of chip (as mentioned in other thread link) but the new firmware IS needed which can extend 510 and rectify connection timeout issues as new firmware for 750 is out.
510 is very versatile Upnp AV product and should evolve. If new firmware for 750 can come, one would assume that 510 would too. Btw, 510 is still in market so users do expect new firmware.