The way I see it, if this thin trend continues in the Pro line of macbooks, Apple is going to inevitably converge on a bit of product ambiguity. I would argue that they already have, especially with the introduction of the new macbook Air model refresh.
It's apparent to me that the Air and Pro line are iteratively becoming the same product after each generational refresh. The new Air is now equipped with a retina display, and dimensions on the newest Air now closely match the dimensions of the Pro models as it were in 2015 while still being ever so slightly thicker than the Pro at its thickest point.
The MacBook product line in 2015 looked a bit like this:
MacBook - Ultra-Ultrabook in lightweight, size, and portability
MacBook Air - Ultrabook in lightweight, size, and portability
MacBook Pro - Power User Pro-level notebook
The vanilla MacBook's main selling point and appeal was its ultra-ultrabook portability and retina display. Drawbacks: Much less powerful, limited ports.
The MacBook Air's main selling point and appeal was its ultrabook portability, battery life, and price point. Drawbacks: Slightly less powerful, no beautiful retina display.
The MacBook Pro's main selling point was portability, battery life, powerful hardware, more ports, etc. Drawbacks: price point.
The current MacBook product line (Q1 2019)
There are some problems for the product line as a whole, since all the products are effectively competing over the same features. The vanilla MacBook is largely unchanged. The MacBook Air is now equipped with a retina display, but the entry price is higher. The MacBook Air is now only $100 less than the base 13" Pro. The only difference is slightly less hardware power. There is no longer a substantial difference in size due to the taper design of the Air in relation to the 13" Pro. The biggest difference in size is only felt ergonomically. The advantage in portability due to size+weight discrepancy is negligible. The MacBook Air, as it was in the state of the product line in 2015 is slightly thicker at the thickest point than the Pro. Technically, the Pro can fit into a smaller enclosure.
Now that the Air has "caught up" with the Pro model in its latest refresh, what separates them now? Hardware, touch bar option, an ever-so-slightly tapered chassis and a 1/4 lb. With a less powerful processor, the Air also enjoys longer battery life (on paper). If we're considering base model to base model, it's a measly $100 difference. With how close they are now, if this trend continues one might reasonably conclude that the next refresh of the MacBook Air and MacBook Pro will result in the exact same product.
What gives?
Customer feedback.
The Pro model gets smaller and more powerful, and the Air model gets more expensive and powerful while matching more features of the Pro. It is clear to me that Apple may have a bit of a disconnect in the department overseeing product development. There are obvious and glaring issues with increasingly more powerful hardware in an increasingly smaller chassis. Currently, the best product on the lineup is hands down the MacBook Air. Apple is simply trying to do too much. To quote the wisdom of my father, you can't shove 10lbs of **** into a 5lb bag. To quote one of my favorite best one-liners ever in cinema from the Blade film, "Some motherf***ers are always trying to ice skate uphill." Why try to do-it-all for every product in your lineup? It doesn't make sense.
Solution:
Pro model
1) Give the power users what they want--More powerful hardware that is respectable for a professional-grade mobile workstation.
2) Do what Apple does best and design that want with the sexiest, slimmest possible chassis and features while respecting the technical limitations that is out of your control in regards to utilizing the most powerful hardware available (Edit: i.e., respect thermal headroom limitations on chassis design). Separate your product line by drawing a line and make the Pro line specific for a professional-grade mobile workstation.
Air model
1) Give the non-power users what they want--The slimmest and sexiest chassis, long battery life, a beautiful display and nominal port expansion for peripheral connectivity.
2) Take your current 13" MacBook Air chassis and scale it to a 15" MacBook Air model.
Now, power users and professionals have a reliable platform option for their needs in the Pro lineup and others have an alternative option for a larger, slimmer MacBook Air in a 15" version. These users don't need the beefy hardware professionals do. There's a clear market here, why aren't you adapting the product line to simply target it instead of converging on a one-size-fits-all solution that makes tradeoffs on the most important use cases for each type of consumer? That is shoddy product management.