Watch out for 3600G then. I don't know if there's a concrete plan to launch it immediately, but it looks like the additional $20 on it may give you what you need. The Navi should do 4k@60.
I realize that this proofs you from getting a PCIe 4.0 GPU of your choice much later, when you have the budget for it.
Of course, don't expect it to give you ultra level graphics for that small die size and heat dissipation.
I'm somewhat skeptical about the 3600G. The 2400G is already a bit bandwidth starved. Dual 64-bit DDR4 channels simply can't keep up with the CPU plus a large GPU. Adding channels isn't possible without changing sockets. There doesn't appear to be enough room on package for an HBM stack like Intel did with Hades Canyon. Running your RAM at 4400MHz with that 0.5x Infinity Fabric multiplier could probably allow a bump from 11CU to 16CU (or 20CU at lower clockspeed). A decent bump and enough to eat the entire low-end GPU market, but not incredible.
I'm left wanting a heterogeneous next-gen system using shared HBM for everything.
Intel currently sells the i7-8809G. It contains a substrate, 4GB HBM2, 24CU Vega M (14nm), and quad-core (3.7-4.7GHz, 14nm) with a TDP of 95w for an MSRP $546. If the substrate and HBM cost $100, then that's MSRP $446 for quad core plus 24CU GPU.
AMD currently sells the 2400G for $130 (launch MSRP for 3400G is $150). The 1300X (100MHz slower, but double the cache) costs $110 giving us around $20 for the 11CU GPU (the 2200G can be had for about $90 indicating the GPU price may actually be lower than that).
Let's build a next-gen APU for both desktop and gaming laptops.
HBM3 spec was finalized almost 3 years ago. Estimates for Vega put 2 HBM2 chips (8GB) at around $150 with a substrate adding another $25. We'll actually work within the constraints of HBM 2 at the moment. Just realize you should get 2x the RAM for around the same price (die shrinks and advances in 2.5D chip construction) along with lower voltages, higher speeds per pin, and potentially fewer stacks needed. We'll use HBM because it has enough bandwidth and uses simpler memory controllers while also cutting latency in HALF vs DDR [latency source](http://www.pdsw.org/pdsw-discs17/slides/stocksdale-pdsw-disc...).
We'll need 16GB of HBM2 at a cost of $300 (remember, that should become 32GB of HBM3 or lower costs closer to $150 for 16GB). If we cost $20 for 11CU, we'll assume $100 for 40CU (adding around a 25% markup for the larger chip though 36CU and 24CU lasered versions could greatly reduce that). That puts us up to $400. A 3600 6-core CPU is selling at $200. We'll add another $50 to the MSRP just because for a final price of $650.
That is $100 more than the MSRP for the i7-8809G, but has a TON of advantages. It has 2 more CPU cores and almost 2x the GPU power (with access to more RAM if it needs). There's no need to spend another $100-200 for additional DDR4 plus the CPU performance will be better due to reduced latency. The lack of RAM on the motherboard and getting rid of all those traces should reduce motherboard cost and size. Finally, at 7nm, this should all fit inside a 95w TDP suitable for both desktops and gaming laptops (which usually have 35-45w CPUs plus 50w+ GPUs).
I realize that this proofs you from getting a PCIe 4.0 GPU of your choice much later, when you have the budget for it.
Of course, don't expect it to give you ultra level graphics for that small die size and heat dissipation.