Let's hope we don't get a virus that wipes out several players, we could end up with hardly any interchanges.

Leaving exceptional circumstances in the hands of RFL is a recipe for disaster. Could easily see them letting Saints or Warrington replace players & telling Lesser teams no. No reason medical exemptions couldn't be written into the rule.

Of course being able to pick your matchday team from 21 rather than 19 is also to the advantage of the top teams.

Gives greater flexibility than last year

Maybe but lets see which team bleats "foul" when they lose 3 interchanges or more.

How many teams last season had to play someone outside the current 19 that had to be named? Very few!
The ability to name 21 gives teams a tactical option. So not really sure what the problem is

Well in your refereeing capacity you are never able to see anything. The problem is a total lack of transparency. The rules should be clear & never left to the arbitrary decisions of a few donkeys at the RFL.

If they can write exemptions for dual reg players & those suspended post declaration then they should be able to list ALL other allowable circumstances.

Supposing 2 players are injured in training Friday for a Saturday game. Saturday morning 2 more go down with a virus (Fulham lost Cairney & Sess through illness & unable to play couple of weeks ago) & 1 pulls out as his wife goes into labour, that leaves you with 16 players for match day. If the RFL are going to say they are not allowable exemptions its just plain daft. Or if medical exemptions are allowed, build it into the rules. Illness independently assessed of course.

What's really different to now? You name yr 19, what happened last year if you get 2 injuries in training then a flu virus.
The reason it was brought in was to show some transparency in squad selections after in effect a reserve team turned out in some games.
The naming of 21 allows a bit more flexibility in squad choice for coaches.
As for Fulham losing players am assuming you are talking football?
Apply that situation though, that's 3 from 21 still leaves 18 and you can only play 17.
Cant really see what the issue is

There is no transparency as only 2 exception are included. Everything else is hidden behind an RFL decision. There is nothing in what the RFL have issued that indicates as far as i can see they will make public their decisions & therefore will be subject to speculation.

Are there any other rule changes for next season ?

Apart from shot clock time change, nothing else has filtered down yet.
Previous years cant remember when rule changes filtered through, think it was late january when refs societies got told what effected community game.

Well Championship clubs can register 5 Amateur players. Good way to strengthen your squad without huge impact on the club. Just need to find them.