Yes, it will be definitely available by that time. AWD production starts in early 2018 (
source). My best guess is January 2018. Right-hand drive production will start in summer 2018 (
source). Best guess, Aug 2018.
My best guess for RHD Model 3 is 2019.
We have had official confirmation that UK M3 deliveries are set to begin "
no earlier than H2 2018"
Being as this is "Tesla Time", I suspect this is optimistic, and realistically means first examples to land in customer hands will be December 31st 2018
(If not later, the PD cars were 6 months behind initial promises, despite being on sale in the US). We've seen this over and over here in the UK, where Tesla hold off as long as possible so they have an order backlog ready to unleash should they need it for a particular quarter. Personally I think the M3 will sell so well in California, then the rest of the US, that there will be little pressure in this regard for a
l-o-o-o-o-ng time.
(This isn't necessarily a criticism, it's a smart way to do business from a TSLA shareholder POV, but less than ideal if you are just a regular UK customer.)
As for AWD variants being available in that time frame, it's certainly possible, however I'd expect Tesla to ship as many orders as they can in RWD format first. Only when they need a demand lever will the AWD be released. Tesla will clearly know they will get two chances that way of people upgrading early hence increasing new car sales. Timing will be important, but I can't see Tesla not selling every RWD car they make in the first 18 months.
In contrast I see Jaguar following suit of other similar sized SUV's with launch cars being AWD, then part through model life a cheaper two wheel drive variant being offered.
All of which is a long winded way of saying I believe the IPace will almost certainly beat the M3 (AWD or RWD) to the UK market.