"mainly going to" is correct and usable in written English.
It is an idiomatic phrasal verb which means "to intend to do something". For example: I'm mainly going to focus on improving my language skills this year.
I'm mainly going to tackle this by freecycling all the vehicles.
But if audiences were mainly going to be English-speaking, why would they go to the trouble?
Globalization, it once seemed, was mainly going to give companies in the U.S., Europe, and Japan billions of new customers and plenty of cheap labor.
The NAO found that the increased numbers of disadvantaged students now attending universities were mainly going to lower-ranked institutions – "which risks creating a two-tier system", dividing those from rich and poor backgrounds.
"The ID card and the ID number are mainly going to be used to verify a resident's identity, safeguard people's rights, make it easier for people to organize activities and maintain law and order," Mr. Guo said.
The City of London - the richest wealth-generating region of Europe - also has a high level of poverty among those who actually live there, with the telephone number salaries mainly going to those who commute into it.
As with previous bailouts, the benefits of this one will mainly go to banks.
"We mainly go to the vintage shops up the road, like Cow," said Drobinski.
This amounts to a cut of £26m which mainly goes to not for profit advice providers.
I'd mainly go to my closest friends, because they always help me through it.
Me and my girlfriend Suzanna mainly go to the Cotswolds, Devon, Spain or Italy.
