The cap has increased by 500k.

More interestingly, they have one player exempt from the salary cap with no financial limitation. See marquee signing.

A team can sign as many players as they like, and choose not to register them as part of their super league playing squad (they can play in other tournaments.) as others have said the super league can use the operating rules to then limit which players are put forward for super league using the limitation of player compensation ruling (which is no different to the Olympics requiring amateur status in some sports) - so no it's not illegal.

It should grow with inflation as a minimum

I think the only challenge to a cap came in major league baseball,but it never came to a decision because the league and players compromised with I think they call it a luxury player tax.
This allows the league to set a spending level but allows those clubs that want to spend more to do so by putting an amount equivalent to the amount over spent into a pot that is then distributed to the club's that under spend.
They also have a minimum spend to stop those clubs that would otherwise spend well below the cap and survive of the hand outs from the sport.

There is a development in the round ball game where [url=http://www.bbc.co.uk/sport/0/football/24333604This Fella[/url is on the case.
It may be easier just to read the [url=http://www.financialfairplay.co.uk/latest-news/legal-challenge-to-uefa-ffp-rules-by-bosman-lawyerPress Release[/url at the bottom of the link.

[url=http://www1.skysports.com/rugby-union/news/12321/9126734/aviva-premiership-clubs-will-have-extra-500000-to-spend-on-player-wagesRU Clubs will have extra £500,000 to spend on player wages[/url





So up to 5M + 1 marquee player outside the cap ..
The above is where is won't work in SL.
outside of individual corp. sponsorship deals & central dist monies from Twickenham, they got a 38M a yr deal (3M per club )from the new BT deal.



the current SKY deal with the SL was 90M over 5 yrs split between 14 clubs ( Approx 1M ) , Even with the cake cut 12 ways in 2015 more of the SKY money is being spread out to the Championship to try to make this new structure viable .

the First Utility deal is reported to be 750K per year

RU's Aviva deal:- [url=http://www.theguardian.com/sport/2010/jul/07/premiership-rugby-sponsorship-avivaPremiership Rugby agrees £20m sponsorship deal with Aviva[/url worth > 400 K per club per year.

We all know the Dr wants to spend more ( and can afford it ) . but until the sport can start to attract TV deals & headline sponsorships approaching those of RU I cannot see the Cap being loosened.

The cap, legally, doesn't have to be enforceable.

You want to play the game that the RFL/SL administers; it is a requirement to adhere to the operational rules. Guess where the cap lives; as part of the operational rules.

Another part of the operational rules is, you can't challenge the operational rules.