In the macOS Catalina 10.15.1 developer betas 1 and 2, the assets reveal a rumoured 16-inch MacBook Pro under the codings. The macOS 10.15.1 version is underway in its beta testing stages for a week already.
To begin with, the icon looks similar to the 15-inch MacBook Pro assets in the prior macOS betas. The only difference between the rumoured 16-inch MacBook Pro and the current 15-inch model. The upcoming, larger MacBook Pro has thinner bezels like the 2017 iPad Pro, 3rd generation iPad Air and the 7th generation iPad. The colours of the rumoured MacBook Pro is the same as the current models, which is space grey and silver. Both of these colours are in their asset names of these MacBook Pro models.
A French Apple blog named MacGeneration found the assets evident in the second developer beta of macOS Catalina 10.15.1. These assets consist of a model identifier name of MacBookPro 16,1 in contrast to the current identifier of the MacBookPro 15,1 for 15 inch MacBook Pro models. These MacBook Pro models will be announced at the upcoming October Apple event if Apple is planning to do one this year.
Therefore, the 2019 16-inch MacBook Pro rumours started since February earlier this year with Ming-Chi Kuo saying that the MacBook Pro will come in an all-new design. This larger, yet not the biggest MacBook Pro Apple has ever made, will have thinner bezels to allow in more screen space in the laptop. But it will have the same design aspects to the current 13 and 15 inch MacBook Pro models.