The success of Second Life requires convincing more people to try it, persuading them to stick around, and persuading them to invest in the grid.
While positive and negative press both mean more newcomers to the grid, negative PR brings with it real world complications. Terrorism, sexual ageplay and age verification, banking, gambling, money laundering, copyright issues... it has all flowed through the mainstream media and gathered political attentions, as such things are wont to do.
If newcomers stick through orientation, they arrive on the mainland with a burning question. "What's there to do here?" That's what the new Showcase tab does; gives the tourists somewhere to go. Well, that and keep journalists from finding dens of perversion within half an hour of downloading the client.
The traffic metric was originally intended as an automated way to do this. Human nature being what it is, the metric is gamed (campers, bots) and often leads to places you wouldn't want to take the general public. A number of places benefit from the way traffic currently works - newbies brings $L, and those translate into real world money. Moving the newbie stream risks hitting the current beneficiaries in the wallet. Accusations of favoritism have plagued the Lab for years, and stating that the places appearing in the Showcase are going to be handpicked hasn't helped. If you want to benefit directly from the newbie stream, I suggest you look into advertising at places that'll be featured regularly. I think this will prove to be a far more effective way to encourage entertaining non-commercial builds than paying dwell ever did, with the side benefit of increasing retention. More money flowing, more content (both static and live). It'll also be good for Linden Lab's bottom line, in $L fees, land, and possibly memberships.
There's a growing effort to clean up the image of the mainland. The ability to own mainland parcels is one of the few benefits of membership, and with the percentage and number of residents with membership declining it makes sense to look at the reasons people give for not wanting to own a piece of Linden Lab's continents.
The new rules surrounding adfarms, and the creation of the LDPW look to be direct action relating to this. Individual residents have been interested in the overall feel of the mainland for a long time. Ask Marianne McCann about getting some of the public Linden builds back in good repair. There's been regular talk by vehicle fans in the forums about improving the road system on the mainland.
Many sim owners who rent space on their sims use the lack of things like laggy clubs and ad farms to attract business. Themed builds and active communities are also draws. Adding roads and other features to the mainland doesn't offer them much competition, but themed residential areas like the new Bay City might.
Personally I suspect they don't have much to worry about, unless LL decides to outsource the oversight of their planned communities. Successful themed sims require human oversight, and Linden Lab has shown a very strong preference for automation, conflict avoidance, and a hands-off approach. I expect that they're planning to use peer pressure and the AR system to enforce Bay City's theme, a combination that hasn't been particularly effective in the past. Building and maintaining communities takes time and effort, as anyone who's tried running a venue in SL can vouch for. Once a community has reached its critical mass it sustains itself, but organizing events and solving conflicts takes time and effort.