Pluckley - London Zones 2-6 Travelcard £3908 annual (Rte: Not HS1)
Pluckley - London Zones 2-6 Travelcard £4860 annual (Rte: Plus High Speed)
Pluckley - London Zones 1-6 Travelcard £4224 annual (Rte: Not HS1)
Pluckley - London Zones 1-6 Travelcard £5208 annual (Rte: Plus High Speed)
Ashford Intl - London Zones 2-6 Travelcard £4052 annual (Rte: Not HS1)
Ashford Intl- London Zones 2-6 Travelcard £4860 annual (Rte: Plus High Speed)
Ashford Intl - London Zones 1-6 Travelcard £4052 annual (Rte: Haywards Heath)
Ashford Intl- London Zones 1-6 Travelcard £4368 annual (Rte: Not HS1)
Ashford Intl- London Zones 1-6 Travelcard £5208 annual (Rte: Plus High Speed)
A ticket from Ashford is clearly valid via Pluckley, yes.
A ticket from Pluckley routed HS1 must be valid via Ashford.
Normally, as a ticket to Zones 2-6 is not valid into Zone 1, it is not valid into a London Terminal. However, both Stratford Intl and London St Pancras Intl are not in the Travelcard zones, therefore I am unsure where this ticket is valid to. Is it valid to St Pancras? I am unsure; I don't see why not. It costs more than a HS1 ticket to London Terminals, this is in contrast to other tickets for 'classic lines' to Zones 2-6 that cost less than a ticket to London Terminals.
As for how practical it is to get to Shepherd's Bush avoiding both Zone 1 and avoiding HS1, it's not particularly easy. I'd suggest via Tonbridge/Redhill/East Croydon/Clapham Jn. Journey time is around 2 hours 13 mins from Pluckley. Cost: £3908
However if you are prepared to pay extra for the HS1 ticket, then it's actually quite simple, you 'just' need to change at Stratford, for a direct train to Shepherds Bush. (actually it's slightly more complex as Stratford Intl > Stratford Domestic involves the DLR, which would be valid on your ticket, however this is not yet open so you would need to get a replacement bus for now). If you were going from Ashford, this is the easiest and fastest journey however from Pluckley the advantage of HS1 is lost as you have to get to Ashford. You have to leave Pluckley at 0518 or 0648. The latter gives you 15 mins in AFK (0658-0713), gets you to Stratford Intl at 0742, and until the DLR is finished you need a bit of luck to make the 0759 from Stratford domestic to Shepherds Bush arriving 0849. This gives a 2 hour 1 min journey time if the connection is made. Once the DLR is up and running 17 mins should be plenty, but until then I am unsure, it depends on the bus link. Cost: £4860
If you wanted to avoid HS1 and go via Zone 1 then the simplest change is at Waterloo (walk from the East platforms to the main station), and again at Clapham Jn. Arriving at 0842 the journey time is around 2 hrs 13 from Pluckley however you should usually make it in 1 hour 53 arriving 0822 (due to extra padding for connections at WAT & CLJ). Cost: £4368