Published shortly after the first Transformers live-action film in 2007, IDW's prequel comic for Revenge of the Fallen features a perfect tribute that the movies should have had (and perhaps still could). Depicting the Autobots' earliest days allying themselves with mankind, Transformers: Alliance features Optimus Prime's attempt to further disguise himself to blend in with humanity, resulting in an epic cameo opportunity the films have yet to take advantage of.
Transformers: Alliance was a 4-issue miniseries published by IDW in 2008 written by Chris Mowry and drawn by Alex Milne. Taking place immediately after the defeat of Megatron in the first Transformers film, the Autobots and human soldiers began working together to clear out the rest of the city. Furthermore, they would then begin hunting the Decepticons who had fled and scattered across the globe, eventually forming the Non-Biological Extraterrestrials Species Treaty (aka N.E.S.T). As such, this series sets up the beginning of Transformers: Revenge of the Fallen where Optimus Prime and the Autobots are seen working with N.E.S.T operatives to take out the Decepticons Sideways and Demolisher.
However, the series' first issue sees Optimus Prime creating his own holographic driver in order to blend in with actual cars and human drivers on the road. Serving as an amazing tribute, the hologram in question resembles Peter Cullen, the iconic voice actor who has been the primary voice of Optimus Prime since the very beginning with the original animated series. While it's a fun nod in the comics, a cameo from Cullen in the actual films has yet to be seen (a huge missed opportunity to recognize the dedicated actor).
Seeing as how this prequel comic series is meant to be canon to the films, it stands to reason that a Peter Cullen cameo could still show up in future installments such as the upcoming Transformers: Rise of the Beasts. Having lent his voice talents to various animated series, movies, and multiple video games for almost 40 years, honoring Cullen's vast work as the leader of the Autobots with his own Stan Lee-style cameo is long overdue.
The live-action Transformers films are largely seen as the culmination of the entire franchise. As such, it's only right that this Peter Cullen tribute in the canonical comics should be adapted for the movies. Regardless of whether the films take advantage of this established cameo opportunity in the future, it's still an amazing idea that perfectly pays tribute to such an iconic character and the actor who's been his voice for decades.