It seems that everything will remain as in the past: Clickair was/is a point to point airline and Vueling will keep this philosophy. IB5xxx cannot be mixed with IBxxxx / AAxxxx / etc. etc., because Clickair is not a OneWorld carrier.
The exception was a couple of VLC-LHR flights operated by Clickair, that have 3 codes: XG, IB5, and IB7. In the case of IB7, connections are allowed. Even if in principle Clickair was suppose to extend the IB7 code to all its flights to/from London Heathrow (in order to make OneWorld connections possible), they never extended the code, and only connections on Clickair are possible for travellers holding a IB7-coded VLC-LHR ticket. This has some explanations, mainly costs, since connections mean $ in terms of aircrafts having to wait for a delayed passenger, the costs of reallocation of passengers, baggage handling, and also the necessity to adapt the Spain-UK schedule with the UK-World flights.

An Iberia worker told me that evenif the IB7 existed, there was no real possibility to connect because the schedules didn't match with "any" flight. I don't know if this is true, but for sure connections are very limited.

The price is very expensive because actually you get the fare of a 2 stops ticket: VLC-MAD-LHR-LAX/SFO. They put high prices in order to have close to zero connecting passengers on each flight.

One "interesting" (actually one of the best) solution for passengers willing to travel with AA is LAX/SFO-JFK-BCN on AA, and then BCN-VLC on Air Nostrum.

I don't think so. Unless they change, neither Vueling nor Clickair want to be part of OW because they would be obliged to connect with OW carriers (Iberia doesn't want low-cost connecting flights because this would make its hub weaker and Clickair/Vueling don't want it because they wouldn't be able to make 30 min stops at big airports such as BCN, they wouldn't be able to maximize aircraft utilisation if they had to match their scedules with the ones of Oneworld, they would have to compensate the passengers that lost their flights, they would have to give BAEC, AAdvantage, etc. points, .... and this is more cost, and more cost is ).

Also OW would not accept Clickair / Vueling. Some quality carriers following the American low-cost model, such as WestJet, were interested in OneWorld but OW (and particularly some carriers such as BA) were against this kind of partners. Only "Click" (by Mexicana) will enter the alliance being a LCC. Anyway, they are a sui generis LCC, since they offer free food and so on. It's more an ad-intra LCC (lower cost structure) than an ad-extra LCC. They are an "economy plus" carrier more than LCC. Very good quality.

OneWorld was born because of connections and business class passengers, and LCC do not offer that. Maybe they could at some point start a new "category": something as "Oneworld associated airline" or non-full member. This category could include LCC linked to OW such as Vueling, Jetstar, FlyBe, even one former partner such as Aer Lingus, and I think that JAL also has a LCC. This category could basically give points/miles to the OW FFP cardholders and could offer some premium services to the elite categories (for instance, Clickair allows to Iberia Plus Oro and Platino the access to the VIP lounges of Iberia) without having to offer connections, coordinated schedules, etc. However, this is only part of my imagination. It will probably never happen.