Luxury interior? Have you seen the inside of the P1 or of a 911 GT3 RS? Just because the badge says Aston doesn't require it be luxurious on the inside. Also, I think you'll find the weight of the DBR1-2 at a nice and lean 900kg.
Remove the racing fuel tank, the roll cage and the rear wing and trade those for road car accessories and it should have no trouble meeting the 1,000kg weight.
A GT3RS is the same inside as a stock 991, and a P1 is pretty much identical to a 650s/12c. Neither are exactly stripped.
Have you ever seen inside a race car?
This car will require sound deadening, a heating & air conditioning system, a radio, sat nav, electric windows, door locks, central locking, leather interior/dash/steering wheel, carpets, much heavier seats (likely electric), a much more complex (and heavier) exhaust system, likely power brakes (not sure if LMP's have servos), ABS system, ESP system, a cooling system able to operate across a much broader temperature range. Even things like door seals and glass will add significant weight over the LMP. And that's without the specific regulatory requirements needed to make it road legal in all countries they want to sell it in.
Their web site is quoting 1:1 BHP:KG. So it's going to need some sort of hybrid system to make 1,000bhp... and we can see form the P1/LaF/918 that this adds a significant amount of weight.
Plus it will likely need an active suspension system if it's going to work on road and on track... to deliver the aero claims on track it will need to be too low and stiff to ever be usable on a road.
There's barely a car on the road in any class that weighs under 1,000kg for a reason.
1,000kg? £100 says it doesn't weigh less than 1,250kg with fluids (if it ever gets built - see below).
Probably worth noting that LMP cars have to conform to minimum weight limits and road cars don't. I don't see any reason why they can't get the weight of a car like this down to a ton - after all, when they're charging £3million for it they're not too limited on what resources they can use. Quarter of a century ago a McLaren F1 was only a hundred kilos more than that with a naturally-aspirated V12...
See above on the practical challenges.
£3M x 100 units is only £300M of revenue. That's nothing in car development terms, and it's not like Aston are rolling in money - they made a £72M loss in the 2014 tax year... though they might benefit from the fall in Sterling post Brexit.
They will lose money on every one they make.
Personally, I don't think this car will ever be made. I just don't think Aston have the cash to make it.
Publicity stunt IMO.