The 61-year-old star was a co-founding member of the girl group - who had several top 10 hits including the US number one hit single 'Venus' - with Keren Woodward and Sara Dallin, and she recently reunited with formerly estranged Shakespears Sister bandmate Marcella Detroit for the EP Ride Again' and a tour, after not speaking to one another for 27 years.
Siobhan quit Bananarama for the first time in 1988 to form Shakespears Sister, due to creative differences, but she rejoined on-and-off, most recently for a tour in 2017 and 2018, their first in almost 30 years, before departing the group again.
However, the 'Stay' hitmaker hasn't ruled out doing some shows with both Shakespears Sister and Bananarama in the future, though she admitted it would be "a lot of work".
Asked if she would be up for a joint tour, Siobhan exclusively told BANG Showbiz: "Well ... you know I'm old enough to say never say never.
"That would be a lot of work."
The fact Siobhan hasn't ruled out a joint tour is a big deal, as she previously claimed she wasn't told the whole story about Keren and Sara's plans for their comeback and was disappointed in their reunion.
She said: "I didn't want to do it just for a British tour and I went back on the understanding that we were going to take it around the world and maybe do a new single.
"But it transpires that's not what they wanted. They just wanted the British tour."
The singer - who added that she "doubts" she'll ever return to the group again - also claimed she wasn't involved in their comeback record from the start.
She explained: "No. They had that in the can before we did the tour."