That's exactly what heatlock is, LoE on surface 2 and I89 on surface 4.

Imagine two windows with almost identical IGU's except one of them has a LoE coating on surface 2 and the other has a surface 3 or 4 coating.

When the sun is shining directly on those two IGU's, the interior glass is going to be warmer when there is a coating on surface 3 or 4. That's why high solar heat gain coatings are applied to surface 3 - they are warmer in direct sunlight - and I89 is the same on surface 4.

I now hear the chorus in the background shouting "but everyone knows that I89 lowers glass temperature!!", and while it's true that I89 on surface 4 does result in a cooler glass surface, even though it lowers U-value, because it reflects room heat back into the room, that's only true when it's warmer on the inside and cooler on the outside.

When it's warmer on the outside and cooler on the inside, and the sun is cheerfully shining on your windows, having I89 on surface 4 will result in a warmer interior glass surface than you would get with clear glass; using the same reasoning why high solar gain coatings are applied to surface 3 and low solar gain coatings are applied to surface 2. It works.

Is heatlock going to make the home uncomfortable because of the increase in temperature of the inside glass?

That's ultimately your call, but here are a few numbers just for comparison...and please remember that these are generic calculations and that YMWV depending on the physical environment

All calculations are based on 90° outside and sun shining on 3mm over 3mm with 1/2" airspace IGU...

clear glass over clear glass IGU - 91° surface 4

clear glass over 366 on surface 3 - 101° surface 4

clear glass over I89 on surface 4 - 108° surface 4

clear glass over 366 on surface 4 - 130° surface 4 (and since this isn't actually possible, I am only including it as a comparison to I89 on surface 4, and possibly to raise a few eyebrows)

LoE 366 surface 2 over clear glass - 83° surface 4

LoE 366 surface 2 over I89 surface 3 - 84° surface 4 (non-standard, only included as a comparison)

LowE 366 surface 2 over I89 surface 4 - 89° surface 4

Whether that additional 6°, give or take, is significant is up to you, but again keeping in mind that just a few clouds in the sky will affect that result.