I think broadly speaking its pretty hard to predict what direction Chelsea will go over the next 3-4 years. Everything from a climb back to the very top of the game and a prolonged period of mediocrity in the 5-7th place range seems possible to me.
They are changing lots of things within the club, with new directors, new recruitment models, new manager, etc. But change doesn't always lead to good results. Sometimes you make big changes and what you implement turns out to be shit. The initial changes to the club at Arsenal post-Wenger were a total disaster, even though they were supposed to modernize the club in many ways, including a remaking of the scouting, recruitment, and data operations. I won't even get into what happened at United post SAF. Let's just say that the transition from one era to the next is not always smooth and successful.
The level of spending on players also seems very uncertain to me, despite many confident predictions from Chelsea fans about this. What we know is that the club is owned by private equity guys and that they came into ownership broadly believing (and promising) that they would make substantial investments in players in order to attain the on-field success that would help them drive value in terms of revenue and asset growth. That all sounds good from a Chelsea fan perspective. But the two things that are unquestionably true about PE people is that they care about making money above all else and that they are absolutely willing to update their strategy based on new information. If they discover that pouring 150-200m into transfers every summer and carrying a wage bill well above what you'd expect given revenues are not paying off in the way they anticipated, they're not going to just keep throwing good money after bad. They're going to quickly pivot to a new strategy where they focus on smarter spending, lower wage bill, etc.
What I can say with some confidence is that Chelsea had a really bad summer if the goal was to build a new team around younger players. The age profile of Sterling, Koulibaly, and Aubameyang makes no sense for that kind of plan and the wages handed out to some of these guys were reportedly massive. Fofana is the only first team player they signed that really profiles as a key building block for the next 3-4 years yet they spent 280m euro in transfer fees and probably committed like 1.2m pounds per week in wages to the quintet of Sterling/Koulibaly/Auba/Cucurella/Fofana. Combine that with a number of other lingering roster/wage bill headaches - for example, Lukaku looks like he is coming back - and its not the easiest situation for a rebuild.