The future of Tesla (TSLA 1.15%) appears very bright. Some experts believe the company's new robotaxi service could add more than $1 trillion in value by the end of 2026. But there's one challenge few investors are paying attention to. This challenge could swiftly eliminate one of Tesla's most profitable revenue sources.Expect Tesla to lose part of this$2.76 billion revenue sourceIn recent years, nearly every electric car stock has benefited from automotive regulatory credits. These credits are earned unde ...