Looking at the Cas v Hull cup game yesterday, there was some serious player fatigue out there (especially from the Cas players, who looked out on their feet with 15 mins to go.
With the fixtures coming thicker and faster, the clubs with larger squads and those able to effectively rotate their players will be the ones at the top of the pile.

Also, with the table now being based on win percentage, will any clubs try postponing games to help the situation with players and with semi final spots up for grabs, could this affect the final table ?

Ultimately, it's just important to try and make it to the end of the season and hope for a return to normal next year.
However, if aclub is in a position to postpone (effectively cancel) fixtures while occupying a semi final spot, could there be some "dark arts" used ?

I think a lot of this is down to the clubs. There are no reserve fixtures, or Championship games, and the rules regarding the salary cap have been relaxed.

Clubs need to rotate there squads rather than just not bothering with games they can't be bothered with. If a club defaults on a game it should be classed as a loss and the club should be punished.

However, generally I believe that player welfare is something Rugby League as a sport gets massively wrong.

There are what effectively will be back to back "Easter fixtures" for the final four fixtures for each club. Then there's the possible catch up fixtures for Catalans and others who have played less games. There's going to be some very odd results, and keep in mind SL has to keep it's side of the Sky deal for getting through 2020.

The issue here is 3, maybe 4 fold.
Number of games and frequency of games.
Injuries, due to the above but also due to increased number of tackles and the ball being in play for longer during games under covid rules.
Absentees due to covid tests itself, including isolation periods.
Finally, with reserve/academy games not being played and certainly with some fringe / younger players having been furloughed, they cant suddenly play on a Saturday or, whichever day.
Also when a game is postponed because of issues with the opposition, it seem wrong that a team then has to play an extra game in a very short space of time.
I realise that we are in difficult and unprecedented times but, the postponements/missed games could certainly be a major factor in who makes the semi's and ultimately who makes the GF.

Many fewer games are played now though, than in the days of the 14 team Championship, County Cups, Regal Trophy, SCCC and Premiership. Those often played with smaller squads of players. So things aren't that bad. Are they?

Brian McDermott suggested having shorter matches before the restart. I thought it was a good idea then, even more so now. 3 thirds of 20 or 4 quarters of 15.

I hope not. That's a small jump to teams of offence replacing a team of defence, each time the ball changes hand, and who knows what else.