Just my thoughts.

Front-end with BI refers to the front-end applications used for reporting. This includes tools like SSRS, Tableau, Microstrategy and even Excel. Learning to develop in those tools are critical. If they involve you learning a scripting language like VBA for Excel, then that makes perfect sense for a BI developer/architect to learn.

One thing to note, R and Python are becoming integrated pieces with those front-end tools. Ignoring those languages could hinder your ability to be a good BI professional in the future. If you asked me if learning them is critical to the future of BI, I would tell you absolutely they are. Learn both if not just one.

Finally, I would disagree that programming or scripting for the backend with other languages not SQL is limiting to BI developers/architects. I only say that because I am very much against the guys who live in their square boxes relying heavily on SSIS, SSAS and SSRS to do everything. ETL is very much beyond SSIS. It's a system the involves many components both SSIS and non-SSIS. If you're working in those areas, knowing how to leverage more than one technology to develop all those components is extremely important.

I truly do believe learning more than those tools is critical to BI in the future because data platforms and environments are really evolving outside those boxes. For example, working with NoSQL, API's, machine learning and more.