Nice manifold!
I have an older blue thunder manifold. Simple, but works and fits superbly.
I don't see any issue with mounting the IAC remotely. Given all the 'stuff' that has to be mounted on the manifold, it's a relief to have the option to mount the IAC off the manifold. You are effectively introducing a controlled air leak past the throttle plates, so as long as the control is there (so no leaks) there should be no issue in doing this.
I have to disagree with Mike, however. There are some significant advantages to efi and not having an IAC doesn't negate these.
I have an Emerald ECU where the idle speed can be controlled via ignition advance or IAC. Fitting an IAC would be a right pain for me, so I use the ignition idle control. When the throttle value is below a certain value, idle control is in force and is controlled by advancing/retarding the ignition. This is not to say IAC is not better, but it's not the only way.
If, for example, your engine may come under additional loads at idle, for example, an air con compressor kicks in or there is a greater electrical load on the alternator, the IAC will probably control this better as you effectively have a limited range throttle controlled by the ECU. It's interesting to note that some newer fly by wire systems don't need an IAC, as the ECU already has direct control over the throttle plates.
If my manifold had this provision, I'd more than likely fit it. Right now, I'm very happy with the rock steady idle and pick up, so not sure where the tractability concern comes from, however.
Apart from idle control, are there other benefits for an IAC? For example, does it come into play between gear shifts? I'd be interested to find out.
All the best,
Vernon