Trust me when I say this, if management gives rizwan the option to open, he will gladly take it.
If you want to put Abdullah in, then saud needs to go but I think saud is more useful atm.
Putting Rizwan at opening is not something most and me are against it. In fact most of us is suggesting him to open the innings in todays scenario, where Fakhar has lost his form.
But the thing is, that many of us think that discarding Fakhar once and for all would be a mistake. Fakhar is someone who have been losing his technique against pace for some time now. But his skill to play spin still exists. That's why it would a good idea to play him down the order at 5. Here he would come when spin attack is on, and utilize him as scenario demands.
Secondly, you are putting too much trust on a absolutely raw Tayyib. At least Saud and Abdullah have been tested in the tests, Tayyib is nowhere to be found even 6 months ago. Therefore, giving him an important position like no. 5, where you either have to play attacking game, or defensive game if there is a top order fall, is too much to ask especially during world cup seasons. It is not feasible to bring an absolutely newcomer in the team at this moment.
This position should go to someone who is extremely experienced which Tayyib is not at all. Therefore most ideal person to bat in this position is either Chacha or Fakhar. After the world cup, Rizwan can be brought back to his original position, in order to slot Saud, Abdullah and Tayyib together.
After world cup:
Abdullah
Imam
Babar
Saud
Tayyib / Agha (based on pitches)
Rizwan
Shadab
Abrar / Wasim Jnr/ Arshad Iqbal
Haris Rauf / Ihsanullah / Zaman Khan
Naseem / Ihsanullah / Zaman Khan
Shahin / Ihsanullah / Zaman Khan
All three pace trio should be rotated constantly with Ihsanullah / Zaman Khan to preserve them as much as possible.