I doubt that new forum software will attract many new users. Design of forum and software isn't main reason why people signup on forum. Main thing is always content. Yes, some people will start using forum because it will be mobile friendly, will look better and will have more features. But number of such users won't be significant.
As said above, best time of online forums is in past already and now young people prefer social media. Old and big forums will stay strong and popular for many years in future because large number of users. But they will struggle to attract young 18-22 years old people. They consider forums as thing from past and people who use it are boomers as they like to say.
But how many of them are real people who actually read and post here? I think very few of them. Most of them are just bots who will not make even single post.