Based on what I've read, I'd assume their expansion in to pay TV would be a "good" thing. Note the inverted comas
They seem to be leveraging this expansion off of their infrastructure (I stand to be corrected here), so that they can do stuff like pay TV by becoming SA's first cable TV operator, using broadband lines to pipe video to homes. Hence my "good" rating. IPTV uses lots of bandwidth, which should force an infrastructure upgrade (I've heard people speculate on the forums that it's the reason why they increased ADSL speeds to 4mbps).
Whether or not the synergy between their various en devours will lead to them monopolising other areas probably depends on what else they get into. I doubt that they'll kill MultiChoice off, so at worse we'll get a Duopoly in pay TV.
Personally, as a web dev guy, I'm more worried about them getting into IT. If they get their hands on BCX, they'll have too big an advantage over the other IT players. Right now, everyone in the IT community hates Telkom because Telkom's rates put a huge limit on what they can offer customers. If BCX are suddenly able to undercut everyone else's prices because they're getting sweetheart rates from Telkom, everyone is going to gravitate to them. The IT industry is already hyper competitive. A Telkom and BCX merger will probably upset the balance quite dramatically.