Will Naim consider NDX upgrade board support Giga LAN ?

A question, and perhaps an answer - Don't average unmanaged home Ethernet switches struggle to really allow 10, 100 and 1000 Mbit traffic to co-exist without degrading the faster links?

I read somewhere that this is particularly true if you are attempting to use jumbo frames on the Gig links.

So, it's not necessarily about the throughput you need for audio, but if you are streaming hi-def video plus a few other intensive activities having devices that only support 10/100 could slow things down.

Please discuss...

No, switches quite happily negotiate or have set port speeds for each switch port. Therefore Ethernet switch ports can be all at different speeds and not impact each other. That is the whole point of a switch.
Hidef audio hardly stresses a traditional 10 Mbps switch port let alone 1gbps. In short 1 Gbps ports for for audio LAN segments are irrelevant. Fine if it's there because the made in china LAN port chip supports it, but no need for swap out or upgrade, if it's not there already.
Simon

I buy the argument that this is what a switch is supposed to do, but from reviewing numerous work related network issues over the last 10 years I'm forced to conclude that they don't always do exactly what it says on the tin. I'm pretty sure the nice shiny Nexus 7000 we've just installed could manage this, but even it's predecessor the 6513 had backplane restrictions that meant it could not handle all the gig connections running anywhere close to max. So, a £100 consumer switch must have limitations - I guess a bit of benchmarking would prove this.

Sure, a poorly designed switch will have unforeseen consequences like with anything  but not really a Naim issue. You mention backplanes capacity, anfpd that refers to bandwidth throughput before the switch starts to block, again a separate matter.
Technically the consideration is more about frame latency. A quality switch will have three options for it's switch port; store and forward, cut through and fragment free, with cheap consumer device probably only supporting cut through. These are strategies for dealing with whether to switch erroneous frames at the expense of per port latency, but again each port is separate. If the switch supports store and forward, the most reliable switch mode, then the entire frame is stored in memory in the switch before being re transmitted. With cut through, the frame is instantly switched as it is received by the switch. If the switch had no buffer or memory then yes it could congestion the uplink, but it would be an extremely poor design and you woulnt want it in your LAN as it could fill the LAN up with rubbish as it would not be isolating the collision domains which is the primary advantage of a switch, otherwise you might as well use a hub. Again nothing to do with Gig support. Errors would affect the throughput on all ports at all speeds in this sceario.

In the hierarchy of needs, 802.11n support supersedes GigE support - backwards b/g only compatibility definitely throttles bandwidth in an already challenged mode of transmission.

Indeed, wireless is a completely different proposition, as its performance is a bit like an old Ethernet hub, ie only one device can transmit at once, and so your slowest device will hold everything back, and worse older protocols sharing the same radio spectrum as the newer such as 802.11n will force the new protocol to downgrade slightly.
Simon