Red Bull is reportedly dissatisfied with Renault's rate of improvement, with the French engines appearing markedly inferior to its Italian and German competitors.
Red Bull Racing consultant Helmut Marko is interested in switching Red Bull over to using Honda engines as long as Honda makes the necessary upgrades, according to recent reports.
Though there has been no official confirmation yet, word has it from unnamed sources that the only user of Honda's engine next year will be Red Bull's Scuderia Toro Rosso.
STR and McLaren supposedly have plans to trade engine suppliers after the 2017 season, as McLaren clamors for a chance to bring itself further up the grid after three successive seasons of being held back by Honda's power unit.
A recent report by Auto Motor und Sport paints Red Bull as dissatisfied and relegated to third-best by a subpar engine, despite operating a top-tier chassis and fielding two of the finest drivers in the sport.
Red Bull is expected to part with Renault after 2018, and Honda is considered its only alternative. While it may seem dubious to claim that Red Bull Racing is changing over to Honda in 2019, it may not be so far-fetched.
STR will use Honda's power units from 2018 through the last season of the current engine regulations in 2020, according to Motorsport.
Given that Marko is apparently considering Honda over Renault, the addition of this STR contract could be seen as Red Bull's way of testing Honda's viability in a low-risk fashion, warts and all.
Red Bull has further options on the table, one of which is a possible sale of their team. AMuS reports that Red Bull would consider selling its team off if the 2021 engine regulations are found unfavorable. Potential customers include Porsche and the individuals involved in the Chinese Formula 1 team effort.
We do know that Porsche is working on a what could be a future Formula 1 engine, so should Honda fall short of Red Bull's desires, they may have an answer hailing from Stuttgart, come 2021.