Since the new Android Wear you ask yourself the question, how many bluetooth connections can a mobile use at the same time?
Is less more again?
The scenario is: Bluetooth speaker - headphones, a fitness wearable, plus perhaps a GPS sensor ala Adidas Speed_Cell and a heart rate monitor with Adidas X_Cell easily placed (just for the Runner). Since the prices are affordable and the boom of statistics and Fitness gadgets do not end, you can choose from a wide range accessories for your smartphone.
The answer is enthusiastically - for the future, too.
The Bluetooth standard is as designed for small groups of a "main device / master device " and seven (belonging to this group) "slave devices". The "main device / master device" is assumed to reflect the timing of the "frequency hopping" from this group. There are also more complex networks possible, but only as an additional information for you. The above-mentioned Bluetooth scenario with the mentioned devices should therefore connect to all without problems.
Why not connect all devices via Wi-Fi, as with Apple via Airplay between his Mac`s?
Wi-Fi consumes much more energy than Bluetooth. Although the connection via Wi-Fi is faster, but incurred in the tiny amounts of data even in music transfer is not such a big disadvantage as a battery too quickly emptied.
With this in mind,
keep on running!