This configuration is seemingly becoming popular. A rupture plate upstream of a PSV protects against fouling, corrosion, and premature wear.

In a gas case, you would run your PSV analysis per usual, but include the load(s) between the burst plate and and relief valve.

I can't really envision a true liquid packed scenario. This would require placing inert liquid in the line.

A liquid line with a gas-filled cavity between the RD and RV would however be commonplace. How would you estimate loads upon piping?
In my mind, there's an instantaneous impulse applied to the piping at the bursting instance, but also when the fluid halts at the PSV, you'll also have fluid hammer.

As the RD is at a set point below the PSV setting, the PSV need not even fire, but if it does, you have another hammer event upstream the PSV, and then what happens downstream of the PSV is a function of size of pipe and superficial velocity, but the liquid could come out as a mist, one continuous liquid front, liquid slugs, or work as "open" channel flow.

What are your thoughts?

I am also seeing more of these set ups lately.

In my opinion, there is no need to introduce this impulse force hitting the inlet of the PSV because in order to develop an impulse you need to develop a flow/velocity. Since the rupture disk is a dumb device that bursts wide open all of a sudden due to exceeded pressure, then the chances of flow developing upstream of the disc would only occur with two simultaneous conditions: that the pressure immediately downstream of the rupture disk is much lesser (which is actually the case) and that the volume immediately downstream of the rupture disk is large (which is not the case). So in my opinion, that disqualifies the need to apply an impulse force.

As a side note, that is the same reasoning I use when ignoring the impulse force hitting any PSV vertically up upon sudden discharge. Some people add a vertical force there but I see it unnecessary. I only assume unbalanced forces AFTER the discharge of the PSV with my F1 being the kickback force opposite to PSV discharge flow.

What I do think applies to burst disks is the pressure thrust. I apply a vertical force down (assuming rupture disk and piping is vertical) which is produced by the sudden "opening" of the pressurized volume. This force can be tremendous especially on larger diameters. I do not combine this force with any of the other PSV thrust forces. So in those situations, my F1 becomes the axial force down from the burst disk and my F2 becomes the kickback force of the PSV.

My two cents.

I'm inclined to agree with your pair of pennies.

I won't go so far as to say that the dynamic pressure is fully negligible, but using a default DLF of 2 is likely going to cover that base by a good bit.

I suspect that then we're going to be installing more snubbers to protect these lines.