Before when different lines were operated by rivalling companies you got different stations very nearby each other which we've come to realise is a bit of a pain nowadays so I don't know why Woolwich wasn't made as an interchange to Arsenal (I do, to please the developers by having a station on site).
There was at one point potentially not going to be a Crossrail station at Woolwich at all because of lack of funding - until an agreement was reached for the developers to pay for the station box. I do agree though that it would have been far better for passengers the Government to have stepped in and funded a Woolwich Arsenal interchange from the start, instead of a separate station. Apart from anything else, Woolwich Arsenal is where most of the bus stops are, and it's far more conveniently located for the town centre.
Interchange to national rail is already available at Abbey wood as has been said and as far as I know, all trains to call at Arsenal also call at Abbey wood. What is missing is a link to that branch of the DLR which could be solved by a station at city airport (Silvertown) which I'd expect would be more desierable honestly as there were already questions raised as to why it was omitted.
As for the travelator, I doubt it would happen since there's already national rail interchange 1 stop further but I do think it would've been better as an interchange.
Personally I'd have had Crossrail call at Canning Town instead of Excel, which would have fixed the problem of not connecting to that DLR branch AND given the connection with the Jubilee line AND given better connections with far more bus routes. But too late now
I agree with you on the travelator. There's not really anywhere above ground it could go - and given that it's only a few minutes walk between the stations, there's probably not enough benefit to justify the huge cost of building one underground. What I think would however be useful (and maybe in the realms of reasonable expense if funding can be found from somewhere) is a footbridge over the very busy A206 dual carriageway - which is going to be the main barrier for interchange. They have recently built a new pedestrian crossing there but it can still be quite a wait to cross, and it looks to me like there is in principle room to build a bridge there. There are also usually a lot of people normally trying to cross that road even today, with no Crossrail - so clearly, a footbridge would benefit a lot more people than Crossrail passengers alone.
